Below is the explanation of all parameters: 

  1. Username (Mandatory): 
    The username of your account. To get a username please register here.
  2. Password (Mandatory):
    The password of your account.
  3. Type (Mandatory):
    Message type to indicate if the message is text, Unicode, flash, etc
    t : Message to be sent, Must be URL encoded (GSM 3.38 Character encoding).
    tf : Flash (GSM 3.38 Character encoding).
    u : Unicode messages such as Chinese or Arabic.
    uf : Unicode Flash messages such as Chinese or Arabic.
  4. To (Mandatory):
    One or more phone numbers, separated by a comma.
  5. Source (Mandatory):
    The sender name that should appear from.
    - Max Length 18 numeric.
    - Max Length 11 alphanumeric.
    Additional restrictions on this field may be enforced by the SMSC.
  6. Message (Mandatory):
    The body of the SMS message.
    Sending Unicode messages such as Chinese or Arabic needs to have the text encoded in UTF-16BE.
  7. Scheduled (Optional): 
    To schedule the message to send it sometime/date in the future. Time/Date format is : "yyyy-mm-dd hh:mm:ss" Which must be URL encoded. The time must be in GMT.

For further information please check it here.