FF81

Data Record is the constructed template Kernel 2 emits at the very end of its own processing, gathering the transaction data the kernel decided the reader needs to carry forward - the functional counterpart, within Kernel 2's own proprietary tag range (the FF-prefixed private-use space), to what template 77 does for the standard GENERATE AC response in contact and other contactless kernels. Because it's a Kernel 2-specific packaging of data rather than a new data element in its own right, debugging an FF81 problem is really debugging whatever specific field inside it looks wrong, in exactly the way a problem in template 70 is really a problem with one of the fields 70 happens to contain rather than with the template wrapper itself. Scoped to Mastercard PayPass (Kernel 2), a terminal or acquirer host expecting a different kernel's output format won't recognise FF81 at all, which is a kernel-mismatch configuration problem rather than a malformed-data one if it ever shows up unexpectedly in a log. See EMV Contactless Book C-2.