Internal server error "Cannot read properties of undefined" during Google OAuth

I created authentications using Better-Auth and Google as the auth client. I have the correct URL for the authorized JavaScript origins and for the authorized redirect URL and I believe my set up is correct for the middleware authentication. I continue to get an Internal Server Error for POST on my Vercel deployment, and when running this in development I get this (from the terminal):

ERROR [Better Auth]: INTERNAL_SERVER_ERROR TypeError: Cannot read properties of undefined (reading 'map')
    at async middleware (middleware.ts:8:20)
   6 |
   7 | export async function middleware(request: NextRequest, response: NextResponse) {
>  8 |     const session = await auth.api.getSession({
     |                    ^
   9 |         headers: await headers()
  10 |     })
  11 |     if(!session) { {
  
}
 ⨯ [Error [APIError]: Failed to get session]

This is the full function:

export async function middleware(request: NextRequest, response: NextResponse) {
    const session = await auth.api.getSession({
        headers: await headers()
    })
    if(!session) {
        return NextResponse.redirect(new URL('/sign-in', request.url))
    }

    return NextResponse.next();
}

I'm confused as to what's wrong with this function implementation. What do I need to change to correct this error?