If you have problem with sending or receiving SMS or MMS on your mobile phone, please try the following methods.

If you are using Android OS mobile phone,

1. Check your signal: please ensure that you are in the area where you get a good reception. It's important to have both good coverage and reliable signal.

2. Clear the Message app's cache: (1) open Settings, then tap Apps (2) Find and tap Messages (3) Tap Storage (4) Tap Clear cache

3. Restart your phone: restart your phone will allow it to reconnect your phone to the mobile network and clear up any temporary app issues preventing message from being sent.

4. Inspect your SIM card: check that your SIM card is in your mobile device properly inserted. You may remove the SIM and insert it back for testing.

If you are using Apple iPhone, 

1. Check your signal: please ensure that you are in the area where you get a good reception. It's important to have both good coverage and reliable signal.

2. Restart your phone: restart your phone will allow it to reconnect your phone to the mobile network and clear up any temporary app issues preventing message from being sent. 

3. Inspect your SIM card: check that your SIM card is in your mobile device properly inserted. You may remove the SIM and insert it back for testing. 

4. You can check further information from Apple website here.