Welcome to the Sage 200 Support Group on Community Hub! Available 24/7, the forums are a great place to ask and answer product questions, as well as share tips and tricks with Sage peers, partners, and pros.
The Sage UK marketplace offers some add-ons for Sage 200, including "Credit Manager" which can record communications sent out to customers (e.g. Debtors Letters)
You can add memo's on the customer account records & also on the customer transaction already in Sage 200 & have been able to for some years, if you press F1 on either screen the online help will explain how to do this