Five things that can happen when you remote auth

There's effectively five things that can happen when you attempt to go for an external authorization to a transaction endpoint:

1. You can abort the Query before sending because you hit the threshold.
[Our internal error APPLERR_THRESHOLD. See this 2007 post.]

2. You can find that none of the channels are connected.
[APPLERR_MUXDISC]

3. Your request can time out (partner didn't respond in time).
[APPLERR_QUERYHOSTTO – note that depending upon the interface and your mutual agreement with the partner, you may be obligated to send a conditional reversal of the original request via a SAF queue.  See an earlier write-up on SAF here.]

4. The partner can answer you but deny the transaction request.
[Varies by implementation, but in ISO8583, this value is plucked from Field 39 and gets translated into a non-0000 Internal Result Code.  See piece here on result code translation]

5. The partner can answer you with an approval.