Pmt Date

Key Pmt Date in Vanilla Option refers to an optional custom date on which the strike associated with the last exercise date is paid.
It applies only on European options and also on non-Europeans that have Pay at Expiry = true
If omitted, it is set equal to the last exercise date.

Note that this feature is accounted in pricing by first calculating the "naked" option price assuming the strike is paid on expiry and then multiplying that price with the forward discount factor from expiry to payment date as implied by the curve associated with the currency of the strike.
It follows that in the case of fx options a non trivial setting here will make the equivalent option on the inverse fx rate returned by the function Get Equivalent Tradable will generally have a slightly different pv and therefore fail to be truly "equivalent" to the original option.