Before deducting CIS and VAT reverse charge from contractor invoices, ensure you've set up CIS for your business.
You'll then need to set up the contractors customer record.
You can only create CIS contractor records with a UK address and a currency of pound sterling (GBP).
You can't disable a contact for CIS once it's set up. You can still process non-CIS invoices by using different ledger codes.
Create a CIS sales invoice
Set up your own CIS ledger accounts
Create a customer contact