Hi Samuel,
When Payables 9.2B was released, there was a problem in how the details were sorted. This was resolved in a Jan 30, 2017 hot fix for Payables 9.2B, and is also in the official release for Payables 9.3A.
When that fix was being done, it was investigated as to whether this grid could be sorted in alternate ways, such as by Invoice number. It was deemed at the time to be very difficult, but I will pass your clients request on.
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Regards,
Softrak Tech Support