Authorization Code Request: 400 - Invalid redirect_uri when adding query parameters

Hi,

I'm in the process of implementing OAuth 2.0 server flow authentication on my platform which serves multiple organizations with each their specific URL. Thus, on the Authorization Request call, I have to make use of additional query parameters by appending them to the redirect URI and encoding them to redirect my users after a successful authentication. Alas, adding any additional query parameters to my redirect URI gives me a 400 - Invalid redirect_uri error page indicating a mismatch between the redirect URI specified in the call and the one on my application settings.

Here's the redirect URI specified in my application settings:

http://www.amilia.localhost/Ws/ConstantContact/OAuthResponse

Here's the non-encoded redirect URI and appended query parameters I'm sending with the Authorization Request:

http://www.amilia.localhost/Ws/ConstantContact/OAuthResponse?orgId=3049

Here's the complete Authorization Code Request as I'm sending it to your servers with redacted Client ID:

https://api.cc.email/v3/idfed?response_type=code&client_id=<MY_CLIENT_ID>&scope=contact_data&redirect_uri=http%3a%2f%2fwww.amilia.localhost%2fWs%2fConstantContact%2fOAuthResponse%3forgId%3d3049

Here's the C# code responsible for redirecting the user to Constant Contact's servers for the Authorization Code Request:

public void AuthorizationCodeRequest(int orgId)
{
    var apiKey = <MY_CLIENT_ID>
    var redirectParams = $"?orgId={orgId}";
    var redirectUrl = HttpUtility.UrlEncode("http://www.amilia.localhost/Ws/ConstantContact/OAuthResponse" + redirectParams);
            
    var url = $"https://api.cc.email/v3/idfed?response_type=code&client_id={apiKey}&scope=contact_data&redirect_uri={redirectUrl}";

    HttpContext.Current.Response.Redirect(url);
}

With no additional query parameters, the authentication works fine and I'm able to get an Access Token with the returned code but as soon as I add any additional query parameters, I am met with the 400 - Invalid redirect_uri error page. I am not sure as to what I'm doing wrong here as adding query parameters to the redirect URI is supported as specified in the V3 API documentation.