How long has it been since the "Supplier needs payment" showed up on your Dashboard? Usually, when they are at operating at peak performance, they check my item in the day it arrives and then the next day it shows payment is pending. From there it almost always takes 24 hours from the moment that "supplier needs payment" shows up on my account before they "initiate payment" to me. So if they receive an item on Tuesday and check it in, on Wednesday evening I'll get the payment initiated email. But they don't do it on weekends.
A full week