Developer Team invitation form doesn't progress

I have received an invitation to a development team in the Apple Developer Program.

Having filled the form out and completing the image challenge successfully, tapping on continue simply results in the button graying itself out.

The JavaScript console shows the following error when this happens:

{
    code: -4
    data: "Destination unavailable. 500"
    message: "Application error."
}

I have tried this process in Safari, Chromium, as well as on mobile data on my iPhone, and the result is the same each time.

Other messages in the console:

[Warning] 30 console messages are not shown.

[Log]  pm-rpc response recieved at  – "" (widget-a72347aab29cc0b7fb82.js, line 2)
[Log] success - rpc: 'receivePingRequest' (widget-a72347aab29cc0b7fb82.js, line 2)
[Log] will send 'receivePingRequest' for rpc: 'formRendered', number of retries left: 1 (widget-a72347aab29cc0b7fb82.js, line 2)
[Log]  - will send rpc message for 'receivePingRequest' (widget-a72347aab29cc0b7fb82.js, line 2)
[Log]  pm-rpc response recieved at  – "" (widget-a72347aab29cc0b7fb82.js, line 2)
[Log] success - rpc: 'receivePingRequest' (widget-a72347aab29cc0b7fb82.js, line 2)

[Error] Blocked a frame with origin "https://appleid.apple.com" from accessing a frame with origin "https://appstoreconnect.apple.com". Protocols, domains, and ports must match.

[Log] will send 'receivePingRequest' for rpc: 'formRendered', number of retries left: 0 (widget-a72347aab29cc0b7fb82.js, line 2)
[Log]  - will send rpc message for 'receivePingRequest' (widget-a72347aab29cc0b7fb82.js, line 2)
[Log]  pm-rpc response recieved at  – "" (widget-a72347aab29cc0b7fb82.js, line 2)
[Log] success - rpc: 'receivePingRequest' (widget-a72347aab29cc0b7fb82.js, line 2)
[Log]  - will send rpc message for 'formRendered' (widget-a72347aab29cc0b7fb82.js, line 2)
[Log] failure - rpc: 'formRendered', reason: reached maximum retries. (widget-a72347aab29cc0b7fb82.js, line 2)