The Contributor role is required to perform most function app-level tasks.
However Website contributor (at the minimum) is required to deploy the App Services / Azure Functions. Website Contributor role should be able to delete the App Services / Azure Functions (Per RoleDef, Microsoft.Web/sites/*). WebPlan contributor comes in handy when you manage plans for functions running in App service plan.
https://learn.microsoft.com/en-us/azure/role-based-access-control/built-in-roles
I hope this helps!
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