Get workflow transition rule configurations

Using Forge, it would be something like this:

import api, { route } from "@forge/api";

const response = await api.asApp().requestJira(route`/rest/api/3/workflow/rule/config?types= postfunction`, {
  headers: {
    'Accept': 'application/json'
  }
});

console.log(`Response: ${response.status} ${response.statusText}`);
console.log(await response.json());

Note that the URL you posted is missing types, so it’d be https://jay.atlassian.net/rest/api/3/workflow/rule/config?types=postfunction, but you shouldn’t be trying to access the URL directly, only through Forge or Connect apps.