By design, if you have available balance on your Upwork account, we'll draw money from it when you purchase connects. If you don't have sufficient balance, we'll charge your billing method on file. You'll also see a notification about this before clicking Add Connects. You can check this help article for more information.
I know there are forum posts asking if you can do this and they've been solved that you can. What I wanted to know was, how can you do this? How can I use my available earnings to buy connects. I have 1 billing method right now which is my VISA card and it always buys from that.