500 error authenticating Eventbrite

I have a site that has recently dropped it’s Eventbrite connection. When I tried to re- authenticate, I successfully logged into Eventbrite and clicked “allow”. I then got the message “There was a problem authorizing with Eventbrite. Please try again in a moment.”

This is happening consistently, so I checked the logs and have found that the authorisation callback from Eventbrite is getting a 302 redirect to the WordPress login screen, generating a 500 server error.

The same thing happens on 2 different Eventbrite accounts for that website (but a different site on different hosting can access both OK). I have checked it with only TwentySeventeen and Keyring enabled and still get the error.

I assume that the login redirect occurs if the callback falls through the parameter verification? Do you have any suggestions on what might be causing the problem?

Your input would be appreciated.

Thank you

Mandy