I am new to EMV and working on a certification of domestic network. Some of the test cards returns AAC while other returns TC when logging 9F27 despite the transaction was approved from host. We suspect that the issue might be root to the tag 91 (Issuer Authentication Data) which is missing in the host response but as we checked the response of those test card where 9F27 returns TC we realized that they also have no tag 91 in it. My question is, is it safe to ignore the card decision and just follow the host response? What could be the other possible reason for such case?
Never ignore decision of a card. Some additional info you need to understand: