First, you will need a PayPal business account. (If you do not have a business PayPal account, it is a free upgrade and gives you access to your API Signature)
Locating and Requesting Your API Signature
Please follow the link below to assist you in locating your PayPal API Signature...
Copying Your API Signature into Your Auction Account
Once you locate and create your API Signature then you will copy all 3 lines into your auction account via General Setup > Payment Information. (Please make sure to check for extra spaces when you copy and paste the information. Sometimes, the copied information sneaks in extra spaces before or after the API)
If you have any questions please do not hesitate to contact us.  We are happy to help.