Thanks a lot for your answer, it did help ! In the end I did switch to "server to server" credential in the developer console and then manually generated the token myself, it worked so the message about free trial was more confusing than problematic.     

Additionnal information, i'm system admin and connected...  

Hello, I used to use the Adobe analytics API 2.0 via Swagger or postman but this has recently become impossible. And the message displayed seems to be linked to a billing problem rather than a technical bug... Have you ever had this problem? It's suggesting a free trial...