Have the server send the header with a valid value, or, if an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled. code example

Example: Add no cores to fetch

// There were no quick access to mode and credentials to other fetch answers.
// Data you'll be sending
const data = { funny: "Absolutely not", educational: "yas" }

fetch('https://example.com/api/', {
  method: 'POST', // The method
  mode: 'no-cors', // It can be no-cors, cors, same-origin
  credentials: 'same-origin', // It can be include, same-origin, omit
  headers: {
    'Content-Type': 'application/json', // Your headers
  },
  body: JSON.stringify(data),
}).then(returnedData => {
  // Do whatever with returnedData
}).catch(err => {
  // In case it errors.
})