How to change Receipt body text and mail merge fields for Receipt/Letter Template
1. Navigate to the Letter Builder
From the Letter object, click on the Letter Builder Button.
In the list of available fields, locate the field you wish to merge in the receipt body. RIGHT-CLICK, then copy.
In the Rich Text Field for the receipt body, place your cursor where you would like the merged field to go, then RIGHT-CLICK and select paste.
After making all your edits, press SAVE button.