If Receipt Management is enabled in your instance of Luminate Online, normally these receipts can be edited under Setup > Receipt Management. See this article for more information.

Support can confirm if a default template is being used for your receipting. If so, the .pdf receipt being generated is the one built into Luminate Online as the default template. This template is hardcoded into the system and can not be modified by either an Admin or Support staff.

The recommendation is to create and upload a new .pdf receipt template. When configuring the template, you can select the applications for which the receipt is used.