I've been trying to set up an automatic creation to my app, as this: When a user is registered in my app, he is also registered in my constant contact account as a contact. The only problem I'm having is with the Authorization URL. I'm using .NET CORE Redirect(AuthUrl) and my AuthUrl in the same format as the API Docs, but I'm getting this response after redirecting:   https://api.cc.email/v3/idfed?client_id={ID}&scope=contact_data&response_type=code&redirect_uri=http...   Access to XMLHttpRequest at 'https://api.cc.email/v3/idfed?client_id={ID}&scope=contact_data&resp...' (redirected from 'https://localhost:44329/Subscriptions/RegisterNewCustomer') from origin 'https://localhost:44329' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status. ... View more