Why does this Pact test fail even though the request and response look correct?

Why does this Pact test fail even though the request and response look correct?

provider.addInteraction({
  state: 'User exists',
  uponReceiving: 'a GET request',
  withRequest: { method: 'GET', path: '/user/123' },
  willRespondWith: { status: 200, body: { id: 123, name: 'Alice' } }
});

// Consumer sends GET /user/123 with body { id: 123, name: 'Alice' }