If you receipts or other PDF documents generated by Payments2Us are showing the missing image Icon as per the below examples, then try the following steps to resolve:
The fist thing to try is:
If still having issues, then set the "Session Security Level Required at Login" as "--None--" on the users profile that has authenticated Payments2Us. The steps and reason why this happen is documented in "Why does the Annual Statement Attachment preview on Contact comes up blank?"