[missing]identityProviderId Error

dan

So I was implementing a custom google login flow following along with the Docs (https://fusionauth.io/docs/v1/tech/apis/identity-providers/google). So my client app has a google auth button and it basically triggers the pop up and the user signs up/logs in. This is not related to FusionAuth yet until I send the id_token from that successful login , which I successfully received and logged, to the /api/identity-provider/login endpoint as stated in the docs. In my POST request, I include all the required information including the id_token, applicationId, and the identityProviderId for Google straight from the docs and my provider instance in my FusionAuth dashboard as you can see below.

fetch("http://localhost:9011/api/identity-provider/login", {
  method: "POST",
  body: JSON.stringify({
    data: {
      token: "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
    },
    identityProviderId: "82339786-3dff-42a6-aac6-1f1ceecb6c46",
    applicationId: "XXXXXXXXXXXXXXXX",
  }),
})
  .then((res) => res.json())
  .then((result) => console.log(result))
  .catch((err) => {
    console.log(err);
  });

For some reason when I run this from my browser which is CORS enabled and my Fusion Auth application also has Google Provider enabled I get the below error. I have no idea what the actual problem is since I clearly have the identityProviderId listed exactly as how it was stated in the docs. If i remove all the other information from the request I still get the same error. What is very weird is that when I make this exact same request from Postman desktop, it works perfectly and I get back the expected response. What could be the problem here, and why am I getting such an unrelated error which makes it virtually impossible to debug?

{
	"fieldErrors": {
		"identityProviderId": [
			{
				"code": "[missing]identityProviderId",
				"message": "You must specify the [identityProviderId] property."
			}
		]
	}
}

Pulled over from https://github.com/FusionAuth/fusionauth-issues/issues/875

dan

Try adding mode: 'no-cors' to your request to see if that changes your result.

Also, make sure that application/json is the Content-Type header for all requests to the FusionAuth API, unless otherwise specified in the documentation.

Narrator: This resolved the issue.