Hello JasonK108,
Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
I can confirm that wildcards are only supported in the redirect URI at the lowest level subdomain. Wildcards can’t be used to pass query parameters or specify a port.
That being said, we are currently investigating an issue where redirect URIs with a wildcard in the lowest level subdomain work successfully with authorization requests when the wildcard character is included in the redirect URI being sent in the request, but result in a 400 error response when the wildcard character is replaced with a variable. We will post again in this thread as soon as we have an update on this issue.
Please have a look and let us know if you have any other questions!
Regards,
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