Missing "?" in Redirect URI

while trying to integrate my oAuth API with GPTs, I am trying the oAuth Client. The oAuth Callback URL I get from gpt looks like


While prompting me to login to my website the redirect_uri I get is in the following format


Notice that the querystring after callback starts without a question mark. This is prompting my server to say that this is an invalid redirect uri. This seems like a bug on gpt side.
Or am I missing something ?