The amount of credit is on your Nitrado account where you see it now. If you need to renew a PC server or order a new PC server, you can use this for that.
If you get a donate to the Nitrado WebUI, and you have an XBox Server: you will not be able to use it. FOr XBox Servers, you probably should create either a patreon or paypal dination link accounts. I have multiple links depending what platform I am using.