Thanks for posting your question @tummyapplication.
You will need to use a different structure for your Algolia data than the Firebase data. Specifically, you cannot have dynamically generated IDs in the path to the indexable attribute. Instead, you can index the data in Algolia as arrays of objects, and store the menu item ID and menu ID of each object as attributes in each object.
The JSON you send to Algolia would look something like this:
With that structure, you would configure
menu_items.name to be in