Was this the sellers FIRST shipped transaction? If so, it can take up to 30 days from the day you received the item. If you read the forums, all the complaints in regards to payments are from people with their initial shipped transaction as a buyer.
Question regarding that though. If it really does take that long, why wouldn’t they clarify that in the terms? It’s kind of misleading. I’m trying to stay in contact with him to make sure it gets resolved at least so he doesn’t think I’m not trustworthy. I buy and sell on several sites. I’ve never experienced this before.
Your inquiry is for OfferUP to answer. The "30 days" seems to be the average number from the anecotal experiences from the other users (you can search the forum rather efficiently since it allows for boolean search).
The seller knows that YOU DID YOUR PART, as OU would NOT issue the seller the shipping label without your payment.