Dynamics 365 Custom Entity Related to Case SubGrid

Most probably a simple question any help/guidance much appreciated. My problem:

I created a custom entity with a N:1 relationship to a Case.

I created a workflow to create a new record on the custom entity when the status reason on the Case change and also created a sub-grid on the case.

When I manually add a record to the custom entity from the Case it links correctly and display in the related entity Sub-Grid on the case.

However, records created through my workflow does not show up on the Sub-Grid. It is created but not linked to the Case.

  1. Should I include the Case ID or Case Number on the custom entity? I thought it would automatically create the relationship?

  2. How can I make the Sub-Grid on the Case read-only/

Thanks in advance for any assistance/guidance.