Required lookup column

I have followed this template example

In order for this to work, I had to manually insert a cartesian product of person x schedule into the Availability table in order for the “crosstab” grouping to show the full grid.

Many users (probably in mobile) try to update a record but end up inserting a new record with a blank schedule date.

Is there a way to require the schedule lookup column aka make it mandatory?

Dear @Woody_Chin,

The developer of the template, @kennymendes might be able to support you.
For sure Kenny will benefit if you mail him ( a link to access your document and see if a solution can be brought up.

I could imagine that the post of @Lloyd_Montgomery could be of your interest

Kind regards,