You can find Card Sample Numbers on our API Reference.
Here are some Sandbox Bank Account Numbers you can use to test with.
When in Sandbox in Client Portal, some processes will allow you to collect a payment or disburse funds without having to type in Sandbox account numbers. In some cases the number will also be provided (For example: Hosted Checkout Page).
However, some do require including the API.
Any 8 or 11 characters without dashes or spaces
Any 18 digit number
Any 9 digit length