Just FYI, the Relevance AI API is expecting your Authorization header to be formatted as Authorization: Token <your_token>. You didn’t say in your post, but have you tried saving the string Token <your_token> as the API key instead of <your_token>?
I ask because other users are reporting that the API key field doesn’t save your API key (and nor should it if it’s secure; OpenAI will hash it first), and the error you’re getting back from Relevance AI makes it sound like they’re picking up an Authorization header, just not a valid one.