When enabling Azure B2C for a Portal that is invite-only, the registration process is complex for the potential users.
When they enter the portal anonymously and just click sign in, they find a "Register now" link in the Azure login. But they cannot register at all because the portal is invite only
When they click the invite link in the invite email, they get redirected to the redeem invite code page without any fucnctionality. Just have to click "register". Confusing.
One step further in the registration process they find the login form from the B2C user flow. From there they have to click "Register now" to proceed. Also confusing and a reason to stop the registration.
Solution could be:
Redirect the login always to an Azure sign in user flow (without registering)
When redeeming invitation the user is asked if he has already a B2C login. If so, the user is taken to the sign in user flow. If not, the user is taken to the register user flow in Azure
When a user is logged in, but has no access to the particular site; give the user a no-access error mentioning this site is invite only. Instead of the redeem invitation page.