It really sucks that you can't buy top up credits. The only way to increase credits is to change plan. And then when you change plan, any unused credits are lost at the end of monthly cycle. I lost over 2000 credits this way. I am an adhoc user, sometime I need it more, sometime less, I thought if I keep it on low plan, then if demand increases, just top up. But no, the system doesn't allow this and honestly I keep looking for other upscalers, like crystalai etc. to achieve what I want.