Guest users who see a 'header too long' error can clear their cookies or open a private or incognito window and try to sign in again. They must choose the account you used to invite them. Guest users who are already signed in to Google are prompted to choose the account they want to use.Guest users who aren't signed in to Google are prompted to do so.When they redeem your invitation, their experience varies depending on whether they're already signed in to Google: For example, you can add them to your directory via the Microsoft Entra admin center. You can invite a Google user to B2B collaboration in various ways. What is the experience for the Google user?

If your apps authenticate users with an embedded web-view and you're using Google federation with Azure AD B2C or Microsoft Entra B2B for external user invitations or self-service sign-up, Google Gmail users won't be able to authenticate. Starting September 30, 2021, Google is deprecating web-view sign-in support.Please refer to Action needed for embedded web-views. To avoid the issue, we strongly advise you to move Gmail authentications to system browsers before creating any new Google integrations for self-service sign-up. Because system web-views are enabled by default, most apps will not be affected. This issue occurs only if you create Google integration for self-service sign-up user flows or invitations after Jand Gmail authentications in your custom or line-of-business applications haven’t been moved to system web-views. Starting July 12, 2021, if Microsoft Entra B2B customers set up new Google integrations for use with self-service sign-up or for inviting external users for their custom or line-of-business applications, authentication could be blocked for Gmail users (with the error screen shown in What to expect).

My google business sign in