I had never heard of this, so I tried it anyway

> Anyone know why a business would choose to only accept credit not debit cards? Maybe they want to place a temporary charge to verify the card's valid? I don't believe you can do so with a debit card.

That seems completely backwards? Debit interchange fees are usually lower aren't they? and if you run it with a pin as a debit there's almost no charge for the vendor. Definitely weird, as everything I know about the incentives for that go in the other direction for a vendor.

I think I read somewhere that forcing credit cards is a way for the merchant to completely avoid prepaid cards. Though obviously imperfect. Privacy.com had to overhaul their card generation backend a few years ago specifically to handle merchants refusing their single-purpose card numbers due to them being detected as potentially prepaid cards. Though they did do it, so it might work for your case now. I'm sure there's a fraud angle where someone signs up with a cheap prepaid card, runs up a huge bill, and then the business has no recourse. Though I'm not familiar with Lambda Labs or their billing.