JSON MOCKAPI
Docs

Custom Mock Builder

Click on RUN SCRIPT to generate mock data with custom fields
fetch('https://fake.jsonmockapi.com/custom', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
 "number": "number",
 "guid": "guid",
 "firstname": "firstname",
 "middlename": "middlename"
})
})
.then(response => response.json())  
.catch(error => console.error('Error:', error));
API Response:
{}