You can write sender ID at the text box specified as highlighted in the figure below.
Message Sender Name is limited to a maximum length of 12 for numeric and a maximum length of 11 for alphanumeric.
If you wish to add a plus sign ('+') to the sender name, please prefix the plus sign to your sender address while submitting the message, and the plus sign should be URL encoded. Additional restrictions on this field may be enforced by the SMSC.
Please refer to Sender ID restrictions in different countries here, and how to register your Sender ID here.
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