I'm also facing same issue, when i click to pay it take too much time to
process and sometime it work successfully, and most of the time it
throws the 550 error.
it's taking too much time to process a payment also sometime it throws
550 error from https://test.authorize.net/Payment/Api.ashxwhen i make
payment call, i have integrated almost 10-15 payment integration but
only this payment getaway have this type...