You'll need to describe your tables and relationships in more detail.
Generally speaking an invoicing system has one table for the invoices, one for the products or services that might be listed on one of the invoices and a line items table where each record lists one item selected for one specific invoice. The portal on the invoice is usually a portal to this line items (called invoice data in the invoices starter solutions for filemaker 12 and 13).
Is that what you have here?
The descriptions would seem to be data from the products/services table and a new table set up as a copy of the invoices table would seem to also need a related line items table. (and it's important to make clear whether you have duplicated a data source table in "manage | Database | tables" or a table occurrence box in "Manage | Database | Relationships".