What a payable is paid is it a debit or credit?

I am assuming you meant "when" a payable is paid?

A "payable" is a liability to the company, it is something they owe. For example, Account Payable. Liabilities maintain a credit balance, meaning they increase with a credit and decrease with a debit.

In short, when you "pay" the payable, you are decreasing what you owe by the amount paid and therefor will "debit" the payable account.