Too Many Requests for url

Hi,
Since tonight, I have been receiving the following error message during authentication:

429 Client Error: Too Many Requests for url: https://api.personio.de/v1/auth?client_id=XXX&client_secret=XXX

We have been using the API for more than a month and have not yet had any problems with authentication. Moreover, I am not aware that anything has been changed on our site. Strangely enough, authentication works on the page "https://developer.personio.de/reference/post_auth-1".

Best,
Fabio