Commerce 2 how to set to live paypal signature API Credentials
Ok I sussed this out quicker than I expected. So for anyone else having this issue do this..


Login to the merchant account NOT the developer account.
Menu on Top right Click Profile > Profile and settings 
My selling preferences > API access > update
Under Pre-built payment solution > Manage API permission
Under Option 2  > View API Signature
Under View or Remove API Signature expose the fields to show the Credential API Signature, API Username, API Password.


Add these to your PayPal settings in the commerce payment making sure you set this to live.