Keep getting error on GetString about fastjson HOT 1 OPEN

You're using parser.Parse which return a *Value type.
As defined here, *Value type doesn't define a GetString function, only GetStringBytes.

If you want to use GetString, use the top-level function → https://pkg.go.dev/github.com/valyala/fastjson#GetString
Example from the pkg.go.dev documentation :

package main

import (
	"fmt"
	"github.com/valyala/fastjson"
)

func main() {
	data := []byte(`{"foo":{"bar":[123,"baz"]}}`)

	s := fastjson.GetString(data, "foo", "bar", "1")
	fmt.Printf("data.foo.bar[1] = %s", s)
}

from fastjson.