GST paid to customs on imported goods

I have an invoice from an item that I imported from overseas. 6k out of 13K is GST. The balance is freight etc. When I split the invoice down & change the tax code to I (100% GST) for the GST content, Essentials slices the tax amount in half allocating just 3K as GST. Does anyone have any ideas how to fix this?

Thanks, Richard