Intrastat on AR invoice UK to UK

Hi all,
I am having an issue with an invoice for a UK customer but the two lines added on the SO as custom parts are now triggering an error message that prevents the posting of the invoice claiming intrastat codes are required for these two lines.
Of course this happens on month end and I need to post this asap.

I believe the easiest way would be to change the lines either on the invoice or on the sales order to have the codes required, but I cannot find where to add them. Any ideas?

One of the easiest ways is to use the ‘Intrastat’ button on the AR Invoice Line
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Unfortunately that button is not available on one of the lines and on the other one it prompts the error message because it is not for a European customer so it is not required.

I’ve found the issue. One of the line still had the old UK Tax Liability.
Easy fix with that.