Several reasons can prevent you from receiving an OTP on your phone. These are;

1. You have blocked Promotional messages on your phone from your carrier. This could be any sender ID or all Sender IDs. To correct this issue, you have to enable them by dialing *100# and proceed to enable all sender IDs. Please note that enabling only one sender ID will, at times, not work.
2. You have a full inbox. This causes your phone not to receive SMS. You will have to delete some SMS and ensure you can receive messages on your phone.
3. Poor carrier network reception. To resolve this, ensure you have a good network reception. If for some reason your SMS are delaying, you can temporarily switch to airplane mode, then turn it off after one minute.
4. You have tried to send the OTP more than 3 times. Normally, this will the app to block you for at least 5 minutes. You are required to wait for 5 minutes, then try again.