I noticed that in both the API integration with Integromat and the Google Sheet add-on, the fees are missing from the data. Was this an oversight?
Thanks for posting. I think there's some misunderstanding here, however.
An Invoice has not fees. Of course, if you add a fee as a line-item, and are consuming line-item level data, you'll see the fee, but I suspect you're asking about the processing fee that you pay when you accept a card payment?
From the Invoice's perspective, even if you incur a processing fee, the payment is still in the full amount. Think of it like this: You write an invoice for $100; that creates Income of $100 and an Account Receivable of $100. You then receive a payment of $100 by check, which fully clears the Account Receivable, and adds (Debits) $100 to Bank.
If, instead, you receive payment via an international wire transfer, your bank will ding you maybe $20 to receive the funds - but the invoice is still fully paid, and you did still receive $100 to bank.
Receiving a payment via Wave Payments is similar: The invoice sees $100 paid; $100 is added (Debit) to a payments clearing / money-in-transit account; and then ~$3.20 is charged (Payment Processing Expense) from that account, before the net ~$96.80 is deposited to your bank.
So, no, it is not an oversight that the Invoice has no Fees, because that's not where Fees exist.
Unfortunately, this means you can't currently access the fee data via API, because we have not yet exposed Transactions data (which is where you would pick up the fee). This is something the team will be working on and that will become available in due course. Right now, however, I don't have a timeline.
Sorry I can't be more helpful, but hopefully this at least allows you to understand what is happening with the data you are seeing.