projects.addProjectDomain throws UnexpectedClientError with reused Request in Next.js server runtime

[mgm1313]

Summary

Calling vercel.projects.addProjectDomain() in a Next.js server runtime throws:

UnexpectedClientError: Unexpected HTTP client error: TypeError: Cannot construct a Request with a Request object that has already been used.

This happened for us while implementing storefront domain management in a Next.js app router app.

Version

• @vercel/sdk: 1.19.11
• Node: 24.11.1
• Next.js app router server runtime
• macOS local dev, but the failure appears tied to the runtime/fetch implementation rather than our domain logic

Failing call

await vercel.projects.addProjectDomain({
  idOrName: projectId,
  teamId,
  requestBody: {
    name: domain,
  },
});

This matches the reference implementation pattern from the SDK docs/examples.

Observed behavior

The failure happens inside addProjectDomain() itself, before any follow-up calls or DB writes.

We confirmed this with runtime instrumentation around our flow:

1. Enter provider create function
2. Call projects.addProjectDomain()
3. Immediate throw:
   • name: UnexpectedClientError
   • message: Unexpected HTTP client error: TypeError: Cannot construct a Request with a Request object that has already been used.
   • cause.name: TypeError
   • cause.message: Cannot construct a Request with a Request object that has already been used.
4. No subsequent refresh/status call ran until we bypassed this SDK method

What we found

Reading the generated transport in src/lib/sdks.ts, _do() still does:

const req = await this.#hooks.beforeRequest(context, request.clone());
let response = await this.#httpClient.request(req);

So this looks like a runtime-specific interaction around cloning a body-bearing Request before the actual fetch.

Workaround that fixed it for us

We replaced only this SDK call with a direct REST fetch to:

POST https://api.vercel.com/v10/projects/{idOrName}/domains?teamId=...

using the same JSON body:

{ "name": "example.com" }

With that workaround in place:

• create domain succeeded
• follow-up getProjectDomain() / getDomainConfig() calls still worked through the SDK
• the full feature worked again

So the issue seems isolated to this POST path / transport behavior, not to all SDK usage.