Monero addresses are composed of a string of 95 characters that begin with the number 4. Always make sure that a 4 leads the address you intend to send your XMR tokens to or the transfer will fail.
With Monero, a "Payment ID" is required to associate your transaction with your account. Payment IDs are 64 characters long and should accompany transactions.
If you are depositing XMR, you can find our Monero address and your Payment ID for each wallet on the Bitfinex Monero deposit page.
If you are withdrawing XMR to a merchant or another exchange where all XMR funds deposit to the same address, you will copy the payment ID they provide you and paste it into your “Recipient Payment ID” field on the Bitfinex Monero withdraw page.