The changes I made in a field set have not applied to my receipt letter, why is that?
Make sure you have clicked the Refresh Button on the specific letter you are wanting to update. Make sure the button has been added on the Page Layout.
Note: If you have made any JSON edits in the letter, this will be reverted back to the current field sets. If you need to save the JSON, copy it and then reapply it after the letter has been refreshed.