AAD Guest User Unable to Accept Email Invitation

Hello,

Our end goal is to add the guest users to a SharePoint Site for collaboration. We want them to have access to all contents on the site. While trying to eliminate creating unique permission on contents we want to add them to our AAD as guest users, then add them as members to the site. We decided to go that route is because we are unable to add them to the members group in SharePoint unless they are added to our AAD.

I've sent an AAD guest invite to 6 external user that stated they don't have MS account and out of 4 has been able to accept the email invitation. The issue is now with the other 2 are required to sign in with a password to complete AAD invite. After clicking the accept invitation they are directed to sign in with a password. They have tried their password for the email we've used to invite but still no luck.

After researching MS docs they stated that a one-time passcode would be sent if guest user does not have a MS Account or meet certain criteria. Wouldn't the guest user have been given a one-time passcode versus having to sign in with a password?

We may have to create them as new user in our AAD if we are unable to add them as guest users. I am confused how 4 out of 6 were able to complete the invitation except for these 2 users.

Any advice would be appreciated! : )

Thanks!