If you login to Peoplevine and under Sell > View Transactions, you can filter them out to show Declined Order transactions. 

When clicking on the transaction you can see the reason it was declined as provided by your payment processor.  If there’s not enough info, then you may need to login to your payment processors gateway to inquire.  Please note that if you see multiple declines, we recommend looking at the 1st one that was processed as it will typically contain more details.