Why do I get HTML when I tried to call my API in my nextjs after using nextAuth

so I’ve been watching tutorial about nextAuthv5, and after finishing the tutorial, I created my own api named appointment and created a simple get method but when I run the code, I received HTML instead of a simple response. It works when I call it on my website(paste the url in google) , but when I tried to call it in my postmark i received an html. I think it affects after changing the middleware.

api/appointment/route.js

export async function GET(request: Request) {
    return NextResponse.json({ msg: 'Hello from server' })
  }

This is my folder structure

 +-- api
 |  |  
 |  +-- appointment
 |      -- route.ts
 |  +-- auth
 |    

middleware.ts


export default auth((req) => {
    const { nextUrl } = req;
    const isLoggedIn = !!req.auth;

    const isApiAuthRoute = nextUrl.pathname.startsWith(apiAuthPrefix);
    const isPublicRoute = publicRoutes.includes(nextUrl.pathname);
    const isAuthRoute = authRoutes.includes(nextUrl.pathname);
    
    if(isApiAuthRoute){
        return ;
    }

    
    if(isAuthRoute){
        if(isLoggedIn){
            return Response.redirect(new URL("/auth/login", nextUrl))
        }

        return ;
    }


    if(!isLoggedIn && !isPublicRoute){
        return Response.redirect(new URL('/auth/login', nextUrl))
        
    }

    return ;
  
})
 
// Optionally, don't invoke Middleware on some paths
export const config = {
    matcher: ["/((?!.+\.[\w]+$|_next).*)", "/", "/(api|trpc)(.*)"],
}

routes.ts

/**
 * Array of routes that are acccessible to the public
 * These routes do not required authnetication
 * @type {string[]}
 */

export const publicRoutes = [
    "/",
    
]
/**
 * Array of routes that are acccessible to the public
 * These routes will redicretct to looged in uesrs to settings
 * @type {string[]}
 */

export const authRoutes = [
    "/auth/login",
    "/auth/register",
    "/auth/error",
    // "/auth/reset",
    // '/auth/new-password'
]

/**
 * The prefix for api authentication routes
 * Routes that start with prefix are used for API 
 * @type {string}
 */

export const apiAuthPrefix = "/api/auth"

/**
 * The default rediect after looging in
 * @type {string}
 */

export const DEFAULT_LOGIN_REDIRECT = "/admin"

This is what I get from my postmark

enter image description here