You can just copy & paste the categories from one sheet to another. No need to use this IMPORTRANGE step. It’s overcomplicating what you’re trying to achieve here.
If you’ve already categorized a bunch of data in the original sheet you can either copy & paste it too from the original sheet to the new sheet or you can try the Labs add-on Migration Helper to get that customized data over into the new sheet (the Categories sheet data too for that matter!)
We don’t have phone support, but you can always write to us using the messenger in the lower right corner of the Console at https://sheets.tillerhq.com/auth/google for issues about the Foundation template or bank data feeds.
We also offer a live weekly webinar that you can attend and ask questions live via the Q&A chat tool or watch a recording of a prior session.