While PUTing subscribers into MailChimp I got a bunch of “Data did not match any of the schemas described in anyOf.” error responses from the API server.
Tried googling, but with no luck.
Second try was to look at the array (data) that was sent.
Array ( [email_address] => email@example.com [status_if_new] => subscribed [merge_fields] => Array ( [FNAME] => John [LNAME] => Doe [COMPANY] => ) )
My thought was that the empty merge field COMPANY was the problem.
So after modifying the code to only send not empty merge field data the error disappeared.