Please follow below steps to troubleshooting the issue.
1.Verify that the user account that is performing this procedure is a member of the db_owner fixed database role in each database.
2.Start SQL Server Management Studio -> Right-click the content database that you want to make read-write -> Click Properties -> Select the Options page, in the Other options list, scroll to the State section -> In the Database Read-Only row, click the arrow next to True, select False, and then click OK.
Reference:
Failed to update database because the database is read-only
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