You configure Azure AD Connect for Azure Active Directory Seamless Single Sign-On (Azure AD Seamless SSO) for an on-premises network.
Users report that when they attempt to access myapps.microsoft.com, they are prompted multiple times to sign in and are forced to use an account name that ends with onmicrosoft.com.
You discover that there is a UPN mismatch between Azure AD and the on-premises Active Directory.
You need to ensure that the users can use single-sign on (SSO) to access Azure resources.
What should you do first?