How can I avoid error 403, "Authorization failed. Please supply a valid auth_key parameter"?
This error occurs when the authentication key in the request is either missing or incorrect.
For the authentication key to be valid, your subscription must be active. You can check your authentication key and the status of your subscription in your DeepL Pro Account, under Plan.
Please also check that you have the correct subscription plan for the usage you require. To get access to DeepL's API, you need to subscribe to the DeepL API plan. The authentication key for CAT tools is included in the DeepL Pro Advanced and DeepL Pro Ultimate subscription plans.