Does Linode charges my balances or promotional credits first?

Hello, I just started using Linode this week, it's been a great journey, the interface and everything is just amazing.

I have added my credits card, I also got my 100$ promotional offer after I signed up, it's natural that I want my nanode plan to charge from promotional offer first.

Here's the deal, I accidentally issued a 5$ payment from my credit card, now it appear on my account balance. I thought Make a payment button was for paying linode services, and then I can pick the promotional credit as payment source.

So what I want to ask is, which payment method does Linode prioritizes, is it $100 free credits or credit card? How do I make it charge on my promotional credit?