Hi there, Alex.
The VAT code 20% RC CIS is used when invoicing for construction services under the Construction Industry Scheme (CIS). However, it's always a good idea to consult with a tax professional or accountant to ensure that you're applying the correct VAT treatment for your specific situation.
HMRC understands that implementing the reverse charge may cause some difficulties. For more details on this change and to learn how it may impact your business, please visit this HMRC page.
Please let me know if you have any follow-up questions with regards to handling VAT in QuickBooks. I'm always here to help. Have a good one.