Suppose we have a PO for GBP 100 and we make partial payments in USD
with fluctuating exchange rates. How should this be handled in Shoebooks?
 
A purchase order doesn't get posted to the GL until it's converted to a bill. Once that occurs, the currency conversion rate all depends on your internal policy regarding how and when to update your currencies rates e.g. When to you manually update your currencies via Setup – Currencies? On a daily / weekly or monthly basis.