Hey everyone,
as already announced in November we are starting to deprecate our legacy authentication methods, rolling out the changes right now.
After the change, if you're trying to authenticate with either an auth_key in query parameter or an auth_key field in the request body you will receive a 403 response.
Read here for more details:
-> https://developers.deepl.com/docs/resources/breaking-changes-change-notices/november-2025-deprecation-of-legacy-auth-methods