I believe you’re facing the same problem as I did. addTask just does not work in 5.3.2 and newer versions.
To login with 5.3.0 you have to delete entries from VersionInfo table in your database via Microsoft SQL Server Management Studio by running this query:
DELETE FROM [your_database_name_goes_here].[dbo].[VersionInfo] WHERE Version > 153
Please note that this is for sure not recommended as you are using a database altered by a newer version of sambapos with an older version of the sw. I did not have any issues on my live setup, though.
I’ve found a workaround to make waiter screen working again without the addTask mutation - just use the add task action.
But I believe someone should look into it and fix it in the next version…