Troubleshooting tips if your SMS are not sending:
Messages will not send if the body exceed the limit of 1600 characters.
If you are using a trigger to send sms. Check the body of message. Also, check to see if there is a custom value of {{message.body}}
Example, if someone replies via email and there email exceed the limit of 1600 characters, the message will not send if you have the custom value {{message.body}}
Other Reasons for SMS Not Sending
Please Note: There is a file size limit of 500mb when attaching videos to SMS messages
Login to https://www.twilio.com/login
Go to the top right -> Click Account -> Click Subaccounts
If there are too many subaccounts inside Twilio, you can go back to HL and copy the Account SIN for that location to search in Twilio:
Search based on the Twilio Subaccount SID in HighLevel agency settings -> Twilio
Paste the Account SID here:
Left panel, Click Monitor -> Errors -> Messaging
Put the lead's phone number (remove all phone format) in the TO field:
Click the Date on the left column for further details:
If it says delivered but the contact is not receiving it, or if there's an error you want to learn further, grab this Message SID and open a ticket with Twilio support

Check if the Twilio number is MMS capable:
Click Phone numbers:
If the phone number is not limited to send/receive calls/SMS to domestic numbers only, and you still can't receive SMS/Calls, please make sure that your Geo permissions are unlocked.
Twilio help article:
HL's Help article on geo permission issue:https://gohighlevelassist.freshdesk.com/support/solutions/articles/48000981435-geo-permissions-issues
'