Trying to log in using Cypress.io, but getting CORS error 'Mismatched Origin'

I'm trying to login to my app using cypress.io, but am getting the error "Mismatched Origin".

According to the documentation, we can bypass CORS by setting chromeWebSecurity:false inside our cypress.json, but I'm still getting CORS errors.

https://docs.cypress.io/guides/references/error-messages.html#Page-Load-Errors

Cypress documentation discourages logging in using the UI, so I'm using the cy.request() method as follows:

Here is my cypress.json file:

{
    "chromeWebSecurity": false,
    "baseUrl": "http://localhost:1234"
}

Here is my test.js file:

      method: 'POST',
      url: 'http://localhost:3000/login',
      body: { 
        username: 'user',
        password: 'password', 
        credentails: 'include', 
        headers: {'Allow-Control-Allow-Origin': "*"}
      }
    }) 

And the error from Cypress:

Status: 400 - Bad Request
Headers: {
  "server": "BaseHTTP/0.6 Python/3.7.9",
  "date": "Thu, 24 Dec 2020 00:49:06 GMT",
  "content-length": "30",
  "content-type": "application/json"
}
Body: {
  "error": "Mismatched origin."
}

I'm wondering if anyone has had luck making a request to a service on a different port to login to in Cypress? Thanks in advance!