Cloudflare Worker: Error: The script will never generate a response

I created a script that puts a list of files into a zip and saves it on in the Cloudflare R2 bucket. The scripts runs until the archive gets closed, after that, it throws the error: Error: The script will never generate a response.

As you see, I catch every possible response, but still, I get this error. Any ideas why?

import { z } from 'zod';
import { ZipWriter, BlobReader, configure } from '@zip.js/zip.js';

// Without this, we get uncaught error due to Workers runtime bug
// See: https://github.com/gildas-lormeau/zip.js/discussions/514
configure({
    useCompressionStream: false,
});

// Payload schema that lists the files to be bundled, their filenames and the archive filename
const schema = z.object({
    archive_filename: z.string().endsWith('.zip'),
    files: z.array(
        z.object({
            r2key: z.string(),
            filename: z.string(),
        })
    ),
});

export default {
    async fetch(request, env, ctx): Promise<Response> {
        // Only POST is supported
        if (request.method !== 'POST') {
            return new Response('Method Not Allowed', { status: 405 });
        }
        const body = await request.json();

        const payload = schema.safeParse(body);
        if (!payload.success) {
            return new Response(JSON.stringify({ status: 'failed', error: payload.error }), {
                status: 409,
                headers: { 'Content-Type': 'application/json' },
            });
        }

        // Use IdentityTransformStream to capture the zip output
        let { readable, writable } = new IdentityTransformStream();

        // Create a ZIP archive stream
        const archive = new ZipWriter(writable);

        // Store all the promises to catch any errors all together later
        let promises: Promise<any>[] = [];

        console.log(payload);

        for (const somefile of payload.data.files) {
            const { r2key, filename } = somefile;
            console.log(r2key);
            console.log(filename);

            // Fetch the file from the R2 bucket
            const fileContent = await env.STORAGE_BUCKET_DEV.get(r2key);
            if (!fileContent) {
                return new Response(`Object not found: ${r2key}`, { status: 404 });
            }

            // Add the file to the ZIP archive
            promises.push(archive.add(filename, new BlobReader(await fileContent.blob())));
            console.log("Item added");
        }

        // Close the archive
        promises.push(archive.close());
        //Everything works till here.


        try {
            // Wait for all files to be added and the archive to be closed
            await Promise.all(promises);

            // Save the ZIP archive to the bucket
            const key = `downloads/${payload.data.archive_filename}`;
            await env.STORAGE_BUCKET_DEV.put(key, readable, {
                httpMetadata: { contentType: 'application/zip' },
            });

            // Return the download URL
            const url = new URL(request.url);
            url.pathname = `/${key}`;
            return new Response(JSON.stringify({ url: url.toString() }), {
                headers: { 'Content-Type': 'application/json' },
            });
        } catch (err) {
            return new Response(
                JSON.stringify({ status: 'error', message: err.toString() }),
                { status: 500, headers: { 'Content-Type': 'application/json' } }
            );
        }

    },
} satisfies ExportedHandler<Env>;