Passing parameter containing special characters to web service methods

Web service does not process parameters with special characters as those can be candidates to dangerous inputs.

So as a workaround you can send the parameters as a query string. That said, the query string should not be too long since there are limitations

For illustration purposes, in the below example JavaScript call I send two variables id & date as method parameters. The address information which is included in variable address1 & address2 are send as  query string.

var restUrl = _spPageContextInfo.webAbsoluteUrl +
            "/_vti_bin/MyService.svc/MyMethod/" + id + "/" + date + "?address1=" + encodeURIComponent(address1) + "&address2=" + encodeURIComponent(address2) ;

Inside your web method access the query string as below:

string address = HttpContext.Current.Request.QueryString["address1"];