Yes, you can absolutely import negative transaction amounts to a Deal. Just enter them as negative ( - or parenthesis) in the import file template you use.
You can also add a description to that line on the import to explain the reason for the reversed amount.
The transaction will appear as debits against the expected payback (increasing balance) on the Deal Tracking page:
For more information on how to upload transactions to deals in MCA Suite using our import template, please see this article. You can also import transactions with a custom format using the report directly from your bank or processor, as long as that template captures the information we need.