Disconnect and reconnect in Settings → QuickBooks, in a browser at gaffermate.co.uk. A connection that's stopped working usually comes back after doing exactly that.
VAT. GafferMate matches your VAT code from your own QuickBooks company file — it doesn't assume 20%. Have a look at the VAT on the first document that lands; every one after that follows the same match.
If it's still wrong after reconnecting, don't keep pushing invoices at it. Email hello@gaffermate.co.uk with what QuickBooks said and it'll be looked at properly.
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