A collection PIN is a unique number that will be generated for each Gumtree purchase. This PIN is the way that you can be sure your money is kept safe until you manage to arrange to collect your purchase from the seller. 

When you collect your purchase from the seller, you will share this PIN with the seller. The seller will enter this PIN on their Gumtree app in order to conclude the sale and release the funds. 

You should ONLY share the PIN when you are physically taking possession of your purchase. Do not share this PIN with the seller until you are happy that you have your purchase and are ready to finalise the sale.