I am attempting to set frame-ancestors dynamically by returning a value from a TRPC route based on the path passed to my middleware function. This is the error I am receiving:

Error [ERR_HTTP_HEADERS_SENT]: Cannot append headers after they are sent to the client

I am a beginner when it comes to middleware and CSP so any tips are appreciated.

middleware.ts:

import { NextRequest, NextResponse } from "next/server";
import { api } from "./trpc/server";

export async function middleware(request: NextRequest) {
  const path = request.nextUrl.pathname;
  const frameAncestors = await api.csp.getSources({ path: path });

  const nonce = Buffer.from(crypto.randomUUID()).toString("base64");
  const cspHeader = `
    frame-ancestors ${frameAncestors};
`;
  // Replace newline characters and spaces
  const contentSecurityPolicyHeaderValue = cspHeader
    .replace(/s{2,}/g, " ")
    .trim();

  const requestHeaders = new Headers(request.headers);
  requestHeaders.set("x-nonce", nonce);

  requestHeaders.set(
    "Content-Security-Policy",
    contentSecurityPolicyHeaderValue,
  );

  const response = NextResponse.next({
    request: {
      headers: requestHeaders,
    },
  });
  response.headers.set(
    "Content-Security-Policy",
    contentSecurityPolicyHeaderValue,
  );

  return response;
}

export const config = {
  matcher: "/some_path/:path*",
};