Problem:
Issue with customers being double charged when using Cayan (apparently it is even more likely when the customer pays with apple pay).
Possible cause:
the problem is that Ivend was timing out while waiting for Cayan to finish . but when it times out the payment has gone through , site then think the transaction has failed and re-do so we get duplicates.
Resolution:
if apple pay is working fine with one of the stores . then need to copy of the cayan dll on problematic stores. citixsys provided the cayan dll .This Cayan dll gave the option to update the timeout to a longer time.