You can pay in-store or thru the site online. However, just be advised that although your payment may show as paid, it may not show as 'credit available' for weeks. I have had this problem several times. I made an online payment thru the 'manage my redcard' site, it came out of my checking account that day but still hasn't been added to my 'credit available'.
However, I made another cash pmyt in store and it showed up within an hour and shows that amt as 'credit available'.
Normally this wouldn't be a problem as I never carry a balance. But I was going to use my credit available to buy more disney gc's for our upcoming trip. uggh. Been almost 2 weeks since pmyt made and still not showing as credit available. Thankfully for me, I also have a debit redcard. So I can just use that to get the cards at a discount.
Just wanted you to be aware of that issue in case it happens to you.