while running the fulfillment event create mutation, this requires that the user must have fulfill_and_ship_orders permission, and i am unable to find out from where and how should this permission should be given to the user.
If you are applying 3rd party to help you fulfill orders, you can ask him to provide you an email address and name for you create a staff account, you will need to authorize him the orders, products and apps access, after that there will be an invitation link sent to the email address, he click the invitation link to activate the account and integrate with ERP on apps store, then the orders in your store can be synced to their erp for automation.