Paris to Cologne (Interrail + 9 Euro Ticket)

I have an unlimited interrail pass for next 2 months. I was wondering how can I use it with the 9 euro ticket if I want to travel from Paris to cologne? I would prefer to not use my interrail journey in Germany since I only have one left.

When I search for Paris - Cologne it shows trains with no connections. Is it possible to change train at France-Germany border and take a regional train to cologne?

Please advise.
Thanks

So I think I can pay 25 euros from Paris to Hergenrath for seat reservation and then buy 7.5 euros ticket from Hergenrath to Aachen HBF and then its 9 euro ticket as long as I stick to regional train. Does this make sense?

The 9 Euro Ticket won’t be valid from Hergenrath to Germany. It’s only usable within Germany, e.g. from the border point to any other point in between. There is a technical border point on this route, that is
„Aachen Süd(Gr)“.

You might be able to travel to this border point with Interrail and continue with the 9€ ticket without buying any other ticket. However, I’m not 100% confident that the 9€ ticket is even valid on this train operated by SNCB. You might have to check this first.

On Aachen - Cologne you shouldn’t have any issue travelling with a local train. From what I see you’d have to leave the TGV in Brussels and continue with Belgian Railway from there to Hergenrath.

There is no station in Aachen Süd (south). The first german station at the railwaytrack from Belgium is Aachen (Hbf/Main Station).

I know. But for every rail that crosses a border, there is a defined border point. There even is a long Wikipedia article about these „Grenztarifpunkte“ which translates to „border fare point“:

However, it might not be possible to purchase a ticket from Aachen Süd (Gr) to Aachen anyway. So the more likely option is to just get a ticket between Hergenrath and Aachen for €4.50