Below is one (or more) of the reasons why the Firstbank USSD code may not be working on your mobile phone.

1. Wrong USSD code: For instance, to transfer money if you type *894*account Number*Amount# instead of *894*Amount*Account Number#, it won’t work
2. Firstbank account and Mobile number are not linked together: Using the Firtsbank USSD code must be the phone number you registered when you opened your Firstbank account.
3. Mobile Network Error: Sometimes the Firstbank USSD code is not working because of issues arising from your mobile network. In this case, try again later or off/on your phone network.
4. FirstBank Network Error: If the USSD code is not working, the issue can be from Firstbank. The only thing to do is to wait till the service is restored.
5. Insufficient Airtime on your Mobile Phone: Your mobile network will charge you for using the Firstbank USSD code except for airtime purchases. Therefore, if you don’t have sufficient airtime, it won’t work.
6. Insufficient Bank Balance: If you do not have sufficient money in your Firstbank bank account including the charges for any transaction, the USSD code will not work.
7. Wrong Firstbank USSD PIN: Another reason why the Firstbank USSD code is not working on your mobile phone is if you are entering a wrong PIN
8. Network Timeout: To successfully use the Firstbank USSD code, you must perform the transaction within some seconds. If you wait too much in between each step, you will get an error message.

You can read this post on Firstbank transfer USSD code and other useful codes