When adding invoices in FE NXT web view, there is not currently a credit memo tile that appears on the add/edit screen of the invoice record. Currently it is possible to apply a credit memo from the credit record accessible from the Vendor's activity.
This will be resolved in the 3/14/18 release of FE NXT.
Steps to Duplicate
1. In FE NXT, Payables > Invoices > Click the + to add a new invoice 2. Notice there is not a tile for Credit memos 3. In payables > Vendors > View a Vendor 4. Under Activity > Click to open a credit memo > Edit 5. There is an area for Open Invoices and it would be possible to apply if there is an open invoice available to be paid/have credit applied