Can't see Linked Customer in a Custom GL Report

I am trying to create a custom report, to replicate the information I used to be able to copy out of my P&L report.  I need to see:

- Cash receipts

- Per chosen GL income accounts

- With the customer

- And the Ref number

I use this information to tally commissions for my sales team.

I have tried to create a custom GL report, but the Linked Customer field is empty. Customers are definitely included in the invoice.

1. How can I get the 'Linked Customer' field to show?

2. If that's too tricky, how else might I run the required information in a way I can get it in to excel?

Screenshot attached.

Thank you in advance.

VIkki