An alternative suggestion:

Import Invoices into Sage 50 - Customer Sales Invoices & Credits (adepttools.co.uk)

Keep a spreadsheet with the necessary information

Note you can export a range of invoices as a starting point.

Every month use search and replace to update the sheet, or create a macro if you want. Then import the new csv

I used this in a previous role and it works like a charm

An alternative suggestion:

Import Invoices into Sage 50 - Customer Sales Invoices & Credits (adepttools.co.uk)

Keep a spreadsheet with the necessary information

Note you can export a range of invoices as a starting point.

Every month use search and replace to update the sheet, or create a macro if you want. Then import the new csv

I used this in a previous role and it works like a charm

I agree. I use Adept invoice importer to do this every month.  Just set up the basic Excel spreadsheet and have every line refer (with an "absolute" reference $) to cells at the top into which you type the date and the variable text.

For example, my Description line for each invoice might be:

="Charges for 4 week period "&$D$1 

where the data in cell D1 is "29/4/24 - 26/5/24"

You can have multiple lines for each invoice as long as each line has a common reference.