You will need to enter the PIN on your Gumtree My Orders page in order to validate it. Only a valid Collection PIN will allow you to get paid. 

We recommend that you enter the Collection PIN that your buyer will share with you during the meetup before releasing your item. We will only release your funds once you have entered the correct Collection PIN. So, you need to ensure that you have been given a valid PIN to know that you will be able to get your funds without and delays.