Read about "post" methods here REST Service Through VDB · GitBook
An example of FORM based call HTML form method Attribute
The way you are doing above in your example is like single Payload, Teiid does not support any parsing capabilities on top of Payload into their respective parameters, that needs to be consumed as is, then if you want you can parse them in your stored procedure into respective parameters. See also how to do multipart/form-data html - What does enctype='multipart/form-data' mean? - Stack Overflow
Further to make myself clear, i'm having 3 parameters in my SP and I'm passing 3 parameters as form/data to call the rest service via post method.
Are you saying, I should have only one parameter in SP (which is like xml) and parse it in SP to get individual parameters and do what is needed?