Routes not found in golang gin

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Go

Golang

I am new in gin golang,
i want to develop api for get course .
but i have a problem in routes.go

when i put this

func Routes(host string) {
	var router = gin.Default()
	router.Use(_c.CORSMiddleware())
	router.Use(_c.RequestHeaderMiddleware)
	router.GET("/grade/courseid:courseid", ggc.GetGradesbyCourseID)
	router.GET("/gradegrades:userid&courseid", ggc.GetDatabyUserID)

	router.Run(host)
}

i can't hit api from postman ,the responses is '404 not found'

but if i use this

<pre>
func Routes(host string) {
	var router = gin.Default()
	router.Use(_c.CORSMiddleware())
	router.Use(_c.RequestHeaderMiddleware)
	router.GET("/grade/courseid:courseid", ggc.GetGradesbyCourseID)
	//router.GET("/gradegrades:userid&courseid", ggc.GetDatabyUserID)

	router.Run(host)
}

it can call it from post man

What I have tried:

is anyone can help me? i wish someone can help me