I sold something and sent it as a large letter. There is rough tracking for it, but no delivery confirmation. The letter should have arrived by now, about 2 weeks ago. But since there is no automatic delivery confirmation, I haven’t received any money. The buyer is not responding to follow-up questions. How do I get my money now?

The buyer can’t help you with that! It may be that payouts in such cases take up to 30 days.