I saw there was a similar issue in the past that supposed to be fixed, but I am still having the same issue.
I am using the Shopify GraphiQL App in my Dev store to test and I am getting the Access Denied error.
Any help here will be much appreciated.
Solved! Go to the solution
just for reference, the link for the other post reporting the same issue, which was reported as a Bug on the Shopify end.
This is an accepted solution.
The GraphiQL app can't be used to test app subscriptions, as it attempts to run the mutation against the GraphiQL app itself (rather than your app). I recommend testing these calls using an HTTP client like Insomnia. To make calls you can install your app on a shop, retrieve the access token from your app, and paste that into Insomnia as a request header.