I filed an amended return, then received a letter from the IRS about an error. No further amendment requested. I owe money, but how do I make the payment? It doesn't say.

The letter has two sort of "vouchers'. One that I should mail if I wanted to appeal their decision, and one that I should mail if I agree and want to pay. I agree and want to pay, but again, nothing on the letter, not an exact figure of the due balance (I can work it out exactly), no mentions of checks, credit cards, nothing. And no balance shown on my IRS profile on their website.