When your gateway device fails to forward messages, the first thing to check is that you have the correct gateway settings, both on the SMS settings page, and on the gateway mobile app. If both your website settings and local gateway are set up correctly, then the you should receive a message 'Integration test passed' when saving the setting on the gateway app. If the test has passed and you still have an issue sending messages, then the issue is more likely to be on your device.
To troubleshoot the issue on your gateway device, here are five things to look at.
Switch to another device: Mobile devices often have hidden software, or non-standard hardware, that can prevent your gateway from working. Trying a different model device is one quick quickest way to resolving gateway issue if they result from such a problem.
Security/ Permission Settings: Check that the local gateway app has the necessary required permissions. This can be viewed in the Phone settings under security> Permissions. (For Android OS 5.0 and above users).
Check your SMS balance: Make sure that you have sufficient airtime/SMS bundle balance.
Cellular Network issues: If there are issues with network coverage in the area, so it is important to check your network signal. Test by sending test SMS from the gateway device to your own local number just to make sure that messages are going through. If not then there might be a network signal issue.When a low signal is indicated, test by calling the gateway from another phone to make sure the device is not off.
Internet Connection: You can troubleshoot your internet connection by googling items on your phone browser to make sure that you are connected to the internet. It is also important to check the internet speed by browsing items: so when your Wifi is slower, you can try switching to mobile data.