FTID means Fake tracking id.
What FTID does is when trying to refund something you can make it look like , lets say if you e.g start a return on walmart or something then you can create a ftid to make it look like you returned the product without actually doing it (sending a placeholder and keeping ur items)
There are multiple different versions of ftid, some being more complicated than others.
FTID v3 is very popular, and is simply just shipping a ftid (e.g an envelope)
if you're looking to refund you can always hire a boxer, I would recommend @Hannibal_ if you're ordering from a company that ships with ups, cause he sells UPS Insider services, which guarantee success rate.