Cannot unmarshal string into Go value of type int64

This is handled by adding ,string to your tag as follows:

type tySurvey struct {
   Id   int64  `json:"id,string,omitempty"`
   Name string `json:"name,omitempty"`
}

This can be found about halfway through the documentation for Marshal.

Please note that you cannot decode the empty string by specifying omitempty as it is only used when encoding.