Capture Invoice Number

I have an invoice which I want to rename based on its content. It's OCR-scanned.

On the invoice it says
Invoice number FEDBG-510-103883467

In the OCR file it says:
Invoice number
FEDBG-510-103883467

I have solved the other aspects of the file name already.

For the invoice number I have selected:

Contents | Content mach | __________________________
What do I have to include in the text field and later in the "Rename with pattern" field?

Other invoices of the same source have similar file names.

macOS Sequoia 15.0.1 / Hazel 6.0.2

Check the manual for "match patterns" for more details. You could have a pattern with "Invoice number" then followed by a custom attribute to match the actual number. You can then use that custom attribute in your actions.