Hi @Tuna_Demirel Welcome!
On Cloud that generic wording is what the AI builder returns when the AI credit pool is empty.
See this:
To check, open the browser network tab and send one message to the builder. If GET /rest/instance-ai/credits comes back 500 while the chat, threads, and preferences calls return 200, the pool is empty. If that call returns 200 and the error still shows, it is server side, so email help@n8n.io with your instance URL and the timestamp of a failed attempt.
Credit allowances per plan are here: