I am building a multi-tenant SAAS app back by Azure AD B2C and using groups as my tenants. I am now building an admin app to manage the tenants and the only people that should be able to use it are the users in my company AD instance. I have created a sign in user flow with my Azure AD as the only Identity Provider and have registered the apps. The user flow works except I get a AADB2C99002 error returned saying I don't exist in the B2C instance. The problem is that I do exist in the B2C instance because I created it and I am the Global Admin for it. I know from the docs it says that you need to sign up first before you can sign in with an external identity provider but like I said I do have an account already and it is linked to my company AD instance.
Can anyone shed some light on why the B2C instance thinks I don't exist?
Right now I am mulling over my options if I can't find out what the issue is. As I see it there are 2 but not sure either will work.
1) create a combined sign up / sign in policy and delete it after I sign up. Not sure if it will create a duplicate user.
2) create a custom sign in policy - not sure if this would fix the problem.