Short list of SMS Gateways compatible with DeskAlerts software

Try removing all the special characters from the number you are using to send the SMS. Furthermore, you might want to check your SMS gateway service account dashboard - most likely, they have a log of API requests here with the exact reasons why messages may not be coming through.

You also need to check sms settings of DA server. For example:

1. For clicksend.com, Gateway URL should be the following: https://api-mapper.clicksend.com/http/v2/send.php?method=http&username=xxxx&key=xxxx&to=%mobilePhone%&message=%smsText%&senderid=Name_of_your_company

You only need to insert your username and key.

2. For smsgateway.ca, Gateway URL should be the following: http://smsgateway.ca/sendsms.aspx?CellNumber=%mobilePhone%&MessageBody=%smsText%&AccountKey=O877FT0Ny0nl4MgeOa070Guh7Ln5QMO 

You only need to insert your AccountKey.

3. Sometimes it is more challenging, for example for www.twilio.com you need to give a link and credential like in example. 

Gateway URL - https://api.twilio.com/2010-04-01/Accounts/Account_SID/Messages.json

Post data - From=Your_phone&To=%mobilePhone%&Body=%smsText%