Trigger Github Actions using the REST API

I am trying to trigger a Github Actions Workflow using the REST API. I’ve added a trigger in the workflow:

on:
  push:
    branches:
      - master
  repository_dispatch:
    types: 
      - build

The API method in question is this one.

I am losing my mind over this. Can somebody tell my, why the following code doesn’t work?

let response = await fetch("https://api.github.com/repos/simse/simse.io/dispatches",
      {
        method: "POST",
        headers: {
          "Accept": "application/vnd.github.v3+json",
          "Authorization": "token [TOKEN]",
          'Content-Type': 'application/json'
        },
        body: JSON.stringify({event_type: "build"})
      }
    )

The API returns a 403. [TOKEN] is a PAT token with repo and workflow scopes.

Worked for me without issue with the provided code. Maybe try a PAT with additional grants?