Hi @Henry_HH,
I’m glad to hear you got it working with the read_all_orders scope, though you should also be able to use it with access scope declaration via the TOML file configuration as well (non-legacy install).
If the app was created via a Partner Account in the Dev Dashboard, for both public and custom apps, you will need to request access to the read_all_orders scope from your Partner Dashboard for that app, before you can declare it in your toml file or legacy authentication calls.
If the app was created via a Merchant Account in the Dev Dashboard however, similar to the legacy Merchant Custom Apps that were previously created in the store’s admin directly, you won’t need to request the read_all_orders scope at all, and the read_orders scope should be sufficient to return all historical orders on the store.
Additionally it’s important to note, that If you added the read_all_orders scope to the app via a new deployed app version with an updated TOML configuration, after it was initially installed, the merchant would then need to open the app in the store’s admin at least once and approve the access scope changes, before the scope is usable in API calls.