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While the option to customise and create categories is unavailable, you'll have to choose the closest category for the transaction. You can refer to this article for more information about disallowable travel expenses.
With regards to your CIS tax, I recommend reaching out to your accountant on how to deduct it from your sales invoices. In addition, the system will record the payment date when you marked the invoice as paid. If it was paid today, you'll have to mark it as paid as well.
The Community space is around to answer your concerns. Have a great day!