Deposits can be returned for many reasons, with the most common reasons being incorrect routing/transit (ABA) numbers and account numbers themselves. Some financial institutions will have member numbers, and while you may use these numbers to log in to the financial institution's services, the numbers are not used as deposit accounts. Some credit unions use a suffix to differentiate a checking account from a savings account.
If you don't know what number to use for your routing number, check your bank's website. If you don't know what number to use for your account number, consult with your bank.