Error: Could not convert argument of type symbol to string.

I also ran into this recently. From what I can tell, at some point (I think in this commit), graphql-request started using the Headers object as opposed to a plain JS object

-   const headers = { ...params.headers }
+   const headers = new Headers(params.headers as HeadersInit)

In my use-case, I was originally modifying and passing headers in a request middleware as such:

const requestMiddleware: RequestMiddleware = async (request) => {
  return {
    ...request,
    headers: {
      ...request.headers,
      Authorization: `Bearer ${await getToken()}`,
    },
  };
};

After the change in the above commit, the resulting headers that are passed look something to the effect of:

{
  headers: {
    Authorization: '<token>',
    [Symbol(headers list)]: HeadersList {
      cookies: null,
      [Symbol(headers map)]: [Map],
      [Symbol(headers map sorted)]: [Array]
    },
    [Symbol(guard)]: 'none'
  }
}

at which point I believe the error is thrown.

For me, I simply changed from spreading the headers to constructing a new Headers object and then using headers.set("Authorization", token).

I'm not sure if this is the same issue as your use-case based on the context provided but thought I'd share

jasonkuhrt / graphql-request

Error: Could not convert argument of type symbol to string. #892

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