PowerApps Custom Connector - blank log-in screen

Hi support,

I'm trying to create a custom connector in Power Apps. Here are the parameters I'm using.

General 

• Host = api.cc.email
• Base URL = /

Security

• Authentication Type = OAuth 2.0
• Identity Provider = General Oauth 2
• Client ID = xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (my api key)
• Secret = ******************************* (my secret)
• Authorization URL = https://authz.constantcontact.com/oauth2/default/v1/authorize
• Token URL = https://authz.constantcontact.com/oauth2/default/v1/token 
• Refresh URL = https://authz.constantcontact.com/oauth2/default/v1/token 
• Scope = contact_data
• Redirect URL = https://global.consent.azure-apim.net/redirect 

When I test the connection, it sends me to this URL (client ID is redacted): https://identity.constantcontact.com/oauth2/aus1lm3ry9mF7x2Ja0h8/v1/authorize?client_id=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx&response_type=code&redirect_uri=https%3a%2f%2fglobal.consent.azure-apim.net%2fredirect&scope=contact_data&state=c01e3d03-a4c1-4564-a899-98fa8eeb51fa_msmanaged-na_azure-apim.net

My web browser opens, but the page is blank. I can't enter anything to get past this step. Any ideas what's going on? Thanks.