MABS SQL Basic availability group backup.

I have Microsoft Azure Backup Server installed on a VM joined to my domain.  I have SQL server 2017 configured with basic availability groups.  I have installed the backup agent on both SQL servers.  When I try to create a protection group I can see the SQL servers and the cluster.  If I open the object SQLc1

All SQL servers

SQL2

Database1

Databse2

I can check mark the databases and add them to a protection group but SQL2 won't always be the primary replica.  I can also open

SQLc1 (Cluster)

Cluster Group

Database1

Database2

I can't select the databases under the cluster for backup.  Is this a limitation of MABS or Basic Availabilty Groups?  How should I configure this so that my database gets backed up?

Thanks