Scope

'Where can I find the error messages for my PayPal transactions?'

'What are the descriptions for the error codes on Paypal?'

'How do I access the list of transactions and the relevant error logs?'

Summary

You can find the error codes and messages in the 'Failed requests' for the PayPal transaction. 

The above link also has details of each error code and its description. 

For a list of transactions follow this.