Hi Brian,
API is Application Program Interface and references the information (data content) sent to ebay by Auctiva at listing submission.
I saw several other posts on this problem recently with one response by Auctiva Tech Support stating the problem was due to the Zip Code on the listing. I assume that's the Zip Code for location of the item. Double-check and see if you have a valid 5-digit numeric zip.
Danno