SMS Gateway not working

SMS Gateway not working

Hello,
I am trying ADSelf Service for my company as a reset tool for our employees , one of the important features that I need is to reset password through SMS , so I contacted my Service provider to send me API access to send SMS in our company name , they sent me the attached document to configure the service , I followed the manual and entered the data as the following :
SMS Provider : Custom 
HTTP Paramater : AccountId=XXXXXXXXX&Password=XXXXXXX&SecureHash=XXXXXXXXXXXXXX&SenderName=OUR COMPANY&ReceiverMSISDN=%mobNo%&SMSText=%message%

After Entering the following Data and trying test SMS I Receive the message unsupported Media type as attached 

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