You should be inputting both a routing number and your account number in separate boxes. Each bank has different account number lengths, so I can't say if 16 digits is the right number for you. But, you should be able to see this information on a copy of any check from that account. It will be at the bottom - generally the routing number will come first and then your account number and then your check number (check sample image below). You DO NOT want to include the check number and 16 digits sounds like you may have included the check number. If your information is incorrect and the IRS is unable to deposit to your account, then they will convert your refund to a paper check and mail to the address on your return.