This is what you need to get it working:

• Pythonista 3 (sadly not cheap, but totally worth in imo)
• YNAB File Import Shortcut
• A personal access token for your YNAB account: help page

Apologies for posting about file based import again, but after recently discovering how useful it actually is, I was greatly dissatisfied with the status quo. So I added file based import to my existing Shortcut, which also still lets you add transactions via Siri, Widgets (or any other way you can trigger Shortcuts).

There's a few variations of the Shortcut:

• The previous version that doesn't require you to buy Pyhtonista, but it had some issues for me, especially when using with Siri.
• A version that let's you add transactions to YNAB and Splitwise at the same time. Here's how that looks like: video
• A more modular version which requires you to have two shortcuts, but also let's you add transactions YNAB File import/Add Transactions (V2)