Why does it ask for my API credentials?
There is precisely NO REASON why one should have to supply one's PayPal API credentials while online. WA should not have any need for that info.
That is a scam and WebAssist obviously cannot be trusted. I find the whole idea abhorrent.
Found on any general site it would be very quickly black listed as a probable phishing scam site.
Having been heavily involved with PayPal for a couple of years until soon after they changed to the new x.com developers areas I advise people to give this new WA freebie a big miss and if installed to DW don't waste time deleting it to avoid the temptation.
Regards, Ron W (PP Wombat)