Getting HTTP response code 400

thanks Roku, But problem occuring here:

param={"abcd":{"isDevice":false,"soapRequest":{"contractAcceptanceMedium":"WEB"}},"searchCustomerProfileRestRequest":{"soapRequest":{"customerSearch":{"address":{"streetAddress1":"UgRnJhbmtsaW4gU3Q=","unitNumber":"NzY0Mg==","zipCode":"MjMyMTk="},"sessionId":""}}},"selectCustomerProfileRestRequest":{"soapRequest":{"sessionId":"","searchSelectionChoice":{}}},"queryBadDebtRestRequest":{"soapRequest":{"sessionId":"","firstName":null,"lastName":null,"emailAddress":null,"socialSecurityNumber":null,"telephoneNumber":null,"creditCheckConsent":false},"dateOfBirth":null}}

when i use :

url.AsyncPostFromString(param)

---->it gives me syntax error in param why? what is wrong in param here.?

if i am not wrong param should be in completely string form here.
According to you

you can post JSON data using AsyncPostFromString(string)

but it does't allow me post my json data here as a parameter. giving syntax error in param.

and Please share an example where we are sending JSON as part of a post request.

Thanks
CPJamloki