HTTP 422 Unprocessable Content (previously Unprocessable Entity) means the server understands the request body format but cannot process the contained instructions. The syntax is correct but the content is semantically invalid — for example, validation errors on form fields.
The request data fails server-side validation — required fields missing, values out of range, or invalid formats.
The request violates business rules (e.g., transferring more money than the account balance).
The 422 response typically includes a list of specific validation errors.
Correct the invalid fields based on the error messages and retry.
Compare your request payload against the API's JSON Schema or documentation.