Why Does My WebRTC Peer Connection Fail in Production with Cloudflare Workers and the OpenAI Realtime API?

I'm building a WebRTC-based real-time application where the browser connects to OpenAI’s Realtime API through a signaling server hosted on Cloudflare Workers using this sample code:
https://github.com/craigsdennis/talk-to-javascript-openai-workers

The setup works fine on localhost, but once deployed in production, the peer connection cannot be established and enters a failed state. Retries do not help.

Here’s what happens step by step:

1. The frontend generates an SDP offer and sends it via HTTP POST to the /rtc-connect endpoint:

JAVASCRIPTCopied
peerConnection = new RTCPeerConnection();

dataChannel = peerConnection.createDataChannel('response');

peerConnection.createOffer().then((offer) => {
            peerConnection.setLocalDescription(offer);
            fetch('/rtc-connect', {
                method: 'POST',
                body: offer.sdp,
                headers: {
                    'Content-Type': 'application/sdp',
                },
            })
                .then((r) => r.text())
                .then((answer) => {
                    peerConnection.setRemoteDescription({
                        sdp: answer,
                        type: 'answer',
                    });
                })
                .catch((error) => console.error("Error in signaling:", error));
        });

2. The Worker relays the SDP offer to OpenAI’s Realtime API.
3. The browser sets the remote SDP description and exchanges ICE candidates with OpenAI.

The server-side code in the Worker is as follows:

JAVASCRIPTCopied
   app.post('/rtc-connect', async (c) => {
        const body = await c.req.text();
        const url = new URL('https://api.openai.com/v1/realtime');
        url.searchParams.set('model', 'gpt-4o-realtime-preview-2024-12-17');
        url.searchParams.set('instructions', DEFAULT_INSTRUCTIONS);
        url.searchParams.set('voice', 'ash');

        const response = await fetch(url.toString(), {
            method: 'POST',
            body,
            headers: {
                Authorization: `Bearer ${c.env.OPENAI_API_KEY}`,
                'Content-Type': 'application/sdp',
            },
        });

        if (!response.ok) {
            const errorText = await response.text();
            console.error('OpenAI API Error:', errorText);
            return c.text(errorText, 500);
        }
        const sdp = await response.text();
        console.log('OpenAI SDP Answer:', sdp);

        return c.body(sdp, {
            headers: {
                'Content-Type': 'application/sdp',
            },
        });
    });

I’m wondering what might be causing the production failure. Is there something missing in the SDP negotiation or ICE candidate exchange that works locally but fails on Cloudflare Workers? Any guidance or suggestions would be appreciated.