4xx Client Error

HTTP 409 Conflict

The request could not be completed due to a conflict with the current state of the target resource. This is typically used in situations where the user might be able to resolve the conflict and resubmit.

Common Causes

  • Trying to create a resource that already exists
  • Concurrent edit conflict (optimistic locking failure)
  • Version mismatch during an update operation
  • Conflicting state transition (e.g., publishing an already published item)

How to Fix

  1. 1Fetch the latest version of the resource and retry
  2. 2Resolve the conflict (merge changes) before resubmitting
  3. 3Use conditional requests (If-Match) for safe updates
  4. 4Check for duplicate entries before creating new ones

Example

HTTP 409 Conflict
POST /api/users HTTP/1.1
{ "email": "alice@example.com" }

→ 409 Conflict
→ "A user with this email already exists"

Related Client Error Codes

400

Bad Request

401

Unauthorized

402

Payment Required

403

Forbidden

404

Not Found

405

Method Not Allowed

406

Not Acceptable

407

Proxy Authentication Required

408

Request Timeout

410

Gone

411

Length Required

412

Precondition Failed

413

Content Too Large

414

URI Too Long

415

Unsupported Media Type

416

Range Not Satisfiable

417

Expectation Failed

418

I'm a Teapot

421

Misdirected Request

422

Unprocessable Content

423

Locked

424

Failed Dependency

425

Too Early

426

Upgrade Required

428

Precondition Required

429

Too Many Requests

431

Request Header Fields Too Large

451

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