Partner Center Stuck on login page

The login form is not working. It keeps saying “Must be logged in to see this page.”
The user is correctly synced to wordpress. The API key and ID on ontraport settings are correct as well. But when I printed the response from the api call, this is the result:

[headers] => Requests_Utility_CaseInsensitiveDictionary Object
        (
            [data:protected] => Array
                (
                    [date] => Tue, 29 Jun 2021 23:37:31 GMT
                    [content-type] => text/html
                    [vary] => Array
                        (
                            [0] => Accept-Encoding
                            [1] => Accept-Encoding
                        )

                    [set-cookie] => PHPSESSID=ulc4rrnv4lh8r5k1nv4jt75o24; path=/
                    [expires] => Thu, 19 Nov 1981 08:52:00 GMT
                    [cache-control] => no-store, no-cache, must-revalidate, post-check=0, pre-check=0
                    [pragma] => no-cache
                    [p3p] => CP="IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT"
                    [x-op-benvironment] => production
                    [x-op-dedicated] => API
                    [x-op-pci] => true
                    [cf-cache-status] => DYNAMIC
                    [cf-request-id] => 0afbbba3570000cf34eb231000000001
                    [expect-ct] => max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"
                    [server] => cloudflare
                    [cf-ray] => 6672fbb22a7dcf34-IAD
                    [content-encoding] => gzip
                )

        )

    [body] => {"type":"error","message":"Authentication Error"}
    [response] => Array
        (
            [code] => 200
            [message] => OK
        )

It was working fine before. Now I'm not sure what changed.

The page I need help with: [log in to see the link]