frappe-errors-api

name	frappe-errors-api
description	Use when debugging or handling API errors in Frappe/ERPNext v14/v15/v16. Prevents silent failures and wrong HTTP status codes in REST endpoints. Covers 401 Unauthorized (wrong token format, expired OAuth), 403 Forbidden (missing @whitelist, allow_guest needed), 404 Not Found (wrong endpoint URL), 417 Expectation Failed (validation via frappe.throw), 500 Internal Server Error, CORS issues, CSRF token missing/invalid, rate limit exceeded (429), file upload failures, JSON parse errors in request/response, webhook delivery failures, and timeout on long operations. Keywords: API error, 401, 403, 404, 417, 429, 500, CSRF, CORS, REST,, API call fails, 403 forbidden, CORS error, token expired, endpoint not found, webhook not received. whitelist, webhook, rate limit, file upload, authentication token.
license	MIT
compatibility	Claude Code, Claude.ai Projects, Claude API. Frappe v14-v16.
metadata	{"author":"OpenAEC-Foundation","version":"2.0"}

API Error Handling

For API implementation patterns see frappe-core-api. For permission errors see frappe-errors-permissions.

---

HTTP Status Code Map: Error -> Cause -> Fix

Code	Frappe Exception	When It Happens	Fix
200	—	Success	—
401	AuthenticationError	Bad/expired token, wrong format	Check Authorization: token key:secret or Bearer access_token
403	PermissionError	Missing @whitelist, no role, no allow_guest	Add decorator or grant permission
404	DoesNotExistError	Wrong URL, doc not found, typo in endpoint path	Verify /api/resource/:doctype/:name or /api/method/dotted.path
409	DuplicateEntryError	Unique constraint violated	Check existing records before insert
417	ValidationError	frappe.throw() called	Fix validation logic or input data
429	RateLimitExceededError	Too many requests	Respect Retry-After header; throttle requests
500	Exception (unhandled)	Unhandled server error	Check Error Log; wrap in try/except
503	—	Server overloaded / maintenance	Retry with exponential backoff

---

Authentication Errors (401)

Wrong Token Format

Error:  HTTP 401 Unauthorized
Cause:  Using "Bearer api_key:api_secret" instead of "token api_key:api_secret"

Frappe uses TWO authentication formats — NEVER mix them:

Method	Header Format	When to Use
API Key/Secret	Authorization: token api_key:api_secret	Server-to-server, scripts
OAuth Bearer	Authorization: Bearer access_token	OAuth 2.0 flows
Session Cookie	Cookie from /api/method/login	Browser-based apps

# WRONG — Bearer with API key:secret
headers = {"Authorization": f"Bearer {api_key}:{api_secret}"}

# CORRECT — token keyword for API key:secret
headers = {"Authorization": f"token {api_key}:{api_secret}"}

# CORRECT — Bearer for OAuth access tokens only
headers = {"Authorization": f"Bearer {oauth_access_token}"}

Expired OAuth Token

Error:  HTTP 401 after token was working
Cause:  OAuth access_token expired
Fix:    Use refresh_token to get new access_token

def get_fresh_token(settings):
    """ALWAYS implement token refresh for OAuth integrations."""
    if is_token_expired(settings.token_expiry):
        response = requests.post(f"{settings.base_url}/api/method/frappe.integrations.oauth2.get_token", data={
            "grant_type": "refresh_token",
            "refresh_token": settings.get_password("refresh_token"),
            "client_id": settings.client_id,
        })
        if response.status_code == 200:
            data = response.json()
            settings.access_token = data["access_token"]
            settings.token_expiry = frappe.utils.add_to_date(None, seconds=data["expires_in"])
            settings.save(ignore_permissions=True)
        else:
            frappe.throw(_("OAuth token refresh failed"), exc=frappe.AuthenticationError)
    return settings.access_token

---

Forbidden Errors (403)

Missing @frappe.whitelist()

Error:  HTTP 403 on /api/method/myapp.api.my_function
Cause:  Function exists but lacks @frappe.whitelist() decorator
Fix:    Add decorator — without it, NO external call is allowed

# WRONG — Callable internally but returns 403 via REST
def my_function(name):
    return frappe.get_doc("Item", name)

# CORRECT — Exposed to authenticated users
@frappe.whitelist()
def my_function(name):
    return frappe.get_doc("Item", name)

# CORRECT — Exposed to everyone including unauthenticated
@frappe.whitelist(allow_guest=True)
def public_function():
    return {"status": "ok"}

Missing allow_guest for Public Endpoints

Error:  HTTP 403 for unauthenticated requests
Cause:  @frappe.whitelist() without allow_guest=True
Fix:    Add allow_guest=True — but ALWAYS validate inputs

NEVER use allow_guest=True without input validation — these endpoints are exposed to the internet.

---

Not Found Errors (404)

Common URL Mistakes

Wrong URL	Correct URL	Issue
/api/resource/SalesOrder/SO-001	/api/resource/Sales Order/SO-001	Space in DocType name
/api/method/myapp.my_function	/api/method/myapp.api.my_function	Missing module path
/api/resource/sales_order	/api/resource/Sales Order	Wrong case / underscore
/api/v2/document/Item/ITEM-001 [v14]	/api/resource/Item/ITEM-001	v2 API only in v15+

# ALWAYS URL-encode DocType names with spaces
import urllib.parse
url = f"/api/resource/{urllib.parse.quote('Sales Order')}/{name}"

---

Validation Errors (417)

Every frappe.throw() call returns HTTP 417 by default (unless a specific exception class is provided).

# Returns 417 — generic validation error
frappe.throw(_("Amount must be positive"))

# Returns 417 — with explicit ValidationError type
frappe.throw(_("Amount must be positive"), exc=frappe.ValidationError)

# Returns 403 — PermissionError overrides to 403
frappe.throw(_("Access denied"), exc=frappe.PermissionError)

# Returns 404 — DoesNotExistError overrides to 404
frappe.throw(_("Not found"), exc=frappe.DoesNotExistError)

ALWAYS use the specific exception class so clients can handle error types correctly:

# WRONG — all errors look the same to the client
frappe.throw(_("Customer not found"))  # 417, generic

# CORRECT — client can distinguish 404 from validation error
frappe.throw(_("Customer not found"), exc=frappe.DoesNotExistError)  # 404

---

CSRF Token Errors

Error:  HTTP 403 "CSRF token missing or invalid"
Cause:  POST/PUT/DELETE request without X-Frappe-CSRF-Token header

Rules:

• ALWAYS include X-Frappe-CSRF-Token header for session-based (cookie) auth.
• Token-based auth (Authorization: token ...) does NOT require CSRF token.
• OAuth Bearer auth does NOT require CSRF token.
• The CSRF token is available in frappe.csrf_token in JavaScript or embedded as window.CSRF_TOKEN.

// Browser-side: ALWAYS include CSRF for session-based requests
fetch("/api/method/myapp.api.update", {
    method: "POST",
    headers: {
        "Content-Type": "application/json",
        "X-Frappe-CSRF-Token": frappe.csrf_token
    },
    body: JSON.stringify({data: "value"})
});

---

CORS Errors

Error:  "Access-Control-Allow-Origin" header missing
Cause:  Cross-origin request not configured in site_config.json

// site_config.json — NEVER use "*" in production
{
    "allow_cors": "https://your-frontend.example.com"
}

For multiple origins [v15+]:

{
    "allow_cors": ["https://app1.example.com", "https://app2.example.com"]
}

---

Rate Limit Errors (429)

Error:  HTTP 429 Too Many Requests
Cause:  Exceeded rate limit configured in site_config.json or hooks.py

# hooks.py — rate limiting on whitelisted methods [v14+]
rate_limit = {"myapp.api.heavy_endpoint": {"limit": 10, "seconds": 60}}

ALWAYS handle 429 in external API calls:

def call_with_rate_limit(url, data):
    response = requests.post(url, json=data, timeout=30)
    if response.status_code == 429:
        wait = int(response.headers.get("Retry-After", 60))
        time.sleep(min(wait, 120))  # Cap at 2 minutes
        response = requests.post(url, json=data, timeout=30)
    response.raise_for_status()
    return response.json()

---

File Upload Errors

Error:  HTTP 500 on /api/method/upload_file
Cause:  Wrong content type, file too large, or missing file field

# CORRECT file upload via REST API
import requests

response = requests.post(
    f"{base_url}/api/method/upload_file",
    headers={"Authorization": f"token {api_key}:{api_secret}"},
    files={"file": ("document.pdf", open("document.pdf", "rb"), "application/pdf")},
    data={
        "doctype": "Sales Invoice",
        "docname": "SINV-001",
        "is_private": 1  # 1 = private, 0 = public
    },
    timeout=60  # ALWAYS set timeout for uploads
)

Common upload failures:

• Content-Type must be multipart/form-data (set automatically by files= param)
• NEVER set Content-Type: application/json for file uploads
• Check max_file_size in site_config.json (default 10MB)
• [v15+] allowed_file_extensions restricts file types

---

JSON Parse Errors

Error:  "Failed to decode JSON" or unexpected behavior
Cause:  API arguments sent as JSON string instead of parsed object

@frappe.whitelist()
def update_items(items):
    # ALWAYS handle both string and parsed input
    if isinstance(items, str):
        try:
            items = frappe.parse_json(items)
        except Exception:
            frappe.throw(_("Invalid JSON format"), exc=frappe.ValidationError)

    if not isinstance(items, (list, dict)):
        frappe.throw(_("Expected list or dict"), exc=frappe.ValidationError)

---

Webhook Delivery Failures

Error:  Webhook not firing or returning errors
Cause:  Target URL unreachable, wrong format, or timeout

Debug checklist:

1. Check Error Log for webhook delivery errors
2. Verify target URL is reachable from server
3. Check webhook condition — is it filtering out the event?
4. [v15+] Check Webhook Request Log for delivery status

# Custom webhook with error handling
@frappe.whitelist(allow_guest=True)
def incoming_webhook():
    """Handle incoming webhook with validation."""
    payload = frappe.request.data
    signature = frappe.request.headers.get("X-Webhook-Signature")

    if not verify_signature(payload, signature):
        frappe.local.response["http_status_code"] = 401
        return {"error": "Invalid signature"}

    try:
        data = frappe.parse_json(payload)
    except Exception:
        frappe.local.response["http_status_code"] = 400
        return {"error": "Invalid JSON payload"}

    # ALWAYS return 200 quickly to prevent sender retries
    frappe.enqueue(process_webhook_data, data=data, queue="short")
    return {"status": "accepted"}

---

Timeout on Long Operations

Error:  HTTP 504 Gateway Timeout or connection reset
Cause:  Operation takes longer than proxy/server timeout (typically 60s)

Fix: Use background jobs for long operations:

@frappe.whitelist()
def start_long_operation(filters):
    """NEVER run long operations synchronously in API calls."""
    job_id = frappe.generate_hash(length=10)

    frappe.enqueue(
        "myapp.tasks.run_long_operation",
        queue="long",
        timeout=600,
        job_id=job_id,
        filters=filters
    )

    return {"status": "queued", "job_id": job_id}

@frappe.whitelist()
def check_job_status(job_id):
    """Poll for job completion."""
    from frappe.utils.background_jobs import get_info
    jobs = get_info()
    for job in jobs:
        if job.get("job_id") == job_id:
            return {"status": job.get("status", "unknown")}
    return {"status": "completed"}

---

Server-Side Error Pattern (Standard)

@frappe.whitelist()
def safe_api_endpoint(docname, action):
    """ALWAYS follow: validate -> check permission -> execute -> handle errors."""

    # 1. Validate input
    if not docname:
        frappe.throw(_("Document name required"), exc=frappe.ValidationError)

    # 2. Check existence
    if not frappe.db.exists("My DocType", docname):
        frappe.throw(_("Document not found"), exc=frappe.DoesNotExistError)

    # 3. Check permission
    frappe.has_permission("My DocType", "write", docname, throw=True)

    # 4. Execute with error handling
    try:
        doc = frappe.get_doc("My DocType", docname)
        result = doc.run_method(action)
        return {"status": "success", "data": result}

    except frappe.ValidationError:
        raise  # Let Frappe handle — returns 417
    except frappe.PermissionError:
        raise  # Let Frappe handle — returns 403
    except Exception:
        frappe.log_error(frappe.get_traceback(), f"API Error: {docname}")
        frappe.throw(_("Operation failed. Please try again."))

---

Client-Side Error Handling

// ALWAYS handle errors in frappe.call
frappe.call({
    method: "myapp.api.safe_api_endpoint",
    args: {docname: "DOC-001", action: "approve"},
    freeze: true,
    freeze_message: __("Processing..."),
    callback: function(r) {
        if (r.message && r.message.status === "success") {
            frappe.show_alert({message: __("Done"), indicator: "green"});
        }
    },
    error: function(r) {
        // ALWAYS check exc_type for specific handling
        if (r.exc_type === "PermissionError") {
            frappe.msgprint(__("You lack permission for this action."));
        } else if (r.exc_type === "DoesNotExistError") {
            frappe.msgprint(__("Record not found."));
        } else if (!r.status) {
            frappe.msgprint(());
        }
    }
});

---

Critical Rules

ALWAYS

1. Use specific exception classes in frappe.throw() — enables correct HTTP status codes
2. Set timeout on all external requests — requests.get(url, timeout=30)
3. Validate ALL inputs before processing — whitelisted methods are callable by any logged-in user
4. Log errors before throwing — frappe.log_error() then frappe.throw()
5. Handle error callback in every frappe.call() — silent failures confuse users
6. Use background jobs for operations exceeding 30 seconds
7. Return 200 quickly from incoming webhooks then process asynchronously

NEVER

1. Expose internal errors to users — log traceback, show friendly message
2. Mix token formats — token key:secret vs Bearer oauth_token
3. Retry 4xx errors (except 429) — they indicate client bugs, not transient failures
4. Skip CSRF token for session-based POST requests — results in 403
5. Set Content-Type: application/json for file uploads — must be multipart/form-data
6. Catch exceptions without logging — makes production debugging impossible
7. Hardcode API credentials — use settings.get_password("field") from a DocType

---

Reference Files

File	Contents
references/patterns.md	Complete whitelisted method, webhook, external API patterns
references/examples.md	Full working API module, client integration, external API client
references/anti-patterns.md	15 common API error handling mistakes

---

See Also

• frappe-core-api — API implementation patterns
• frappe-errors-permissions — Permission error handling (403 deep dive)
• frappe-syntax-whitelisted — Whitelisted method syntax
• frappe-errors-serverscripts — Server Script error handling