If you happen to have several entries of the same customer/supplier in your list, you can merge entries together so you only have one entry per customer/supplier.
To do so:
- Go to the Customers & Suppliers menu
- Select 2 or more customers/suppliers then click on Merge customers (or Merge suppliers)
- Pick the one you'd like to keep as the main entry
When done, all documents previously linked to the various entries will be linked to the main customer/supplier. Please note that merging customers/suppliers can't be undone.