There are various reasons why you might not be able to top up your mobile credit
1) You might have insufficient Boost wallet balance. If so, please top up your Boost wallet first before topping up your mobile credit
2) Your prepaid mobile number might be inactive. If your prepaid mobile number is inactive, you will not be able to top up mobile credit until it is reactivated. Please check with your mobile operator whether your number is inactive, and if so, whether they can reactivate it for you
3) There might be an error in your mobile operator's system at the moment, do try again in an hour or so.
If this issue persists, please submit a request and share more details with us. We are happy to help you out!