Permission issue on restore of the db from primary to secondary
Permissions

from https://docs.microsoft.com/en-us/sql/t-sql/statements/restore-statements-transact-sql


  If the database being restored does not exist, the user must have
  CREATE DATABASE permissions to be able to execute RESTORE. If the
  database exists, RESTORE permissions default to members of the
  sysadmin and dbcreator fixed server roles and the owner (dbo) of the
  database (for the FROM DATABASE_SNAPSHOT option, the database always
  exists). RESTORE permissions are given to roles in which membership
  information is always readily available to the server. Because fixed
  database role membership can be checked only when the database is
  accessible and undamaged, which is not always the case when RESTORE is
  executed, members of the db_owner fixed database role do not have
  RESTORE permissions.