Redirect to the same page with flash message and retain user input

[wildfiremedia]

Google isn't help and I couldn't find echo solution.

If a user were to type email and password into a login page and encounter an error when email or password is incorrect.
It would throw a flash message but also retain user email. I can wrote this in Go stdlib and response is Get.

But in Echo, the response is still Post.
return c.Render(http.StatusFound, "views/signin.html", echo.Map{"flashmessage": "Password..", "emailaddress": EmailAddress, "Csrf": helpers.NewCSRF(c)})

How do I redirect to the sign in page and retain user input with Get response instead of Post response?

[baxiry]

just render login page if username or password is not correct

      func login(c echo.Context) error {
      femail := c.FormValue("email")
      fpass := c.FormValue("password")
      user := getUsername(femail)     // User struct
 
      if user.Pass == fpass &&  user.Email == femail {
          // TODO save new session here
          return c.Redirect(http.StatusSeeOther, "/") // 303 code
          // or redirect to latest page
      }
      return c.Render(200, "login.html", "Username or password is wrong")
  }