Moved to
X-Payments issues & questions
This seems to be related to the old "Paypal line items" issue we had in X-Cart (UPDATE: not fixed in X-Cart 4.5.4 you are using).
UPDATE:
I was wrong - it is not fixed in 4.5.4, but we have a patch for the issue for 4.5.4 and also it will be included in the upcoming 4.5.5. Just contact our techs for a free patch using your HelpDesk account. Refer to this post when you submit a ticket.