Send Message Example: 
http://api.text-connect.co.uk/api/api.php?Username=XXXXXXX&Password=XXXXXX&Action=Send&DestinationAddress=447866777777&SourceAddress=TCtest&Body=Message-Body-Here&ValidityPeriod=86400

 
Check Credits Example:
http://api.text-connect.co.uk/api/api.php?Username=XXXXXXX&Password=XXXXXXX&Action=checkcredits