[FMadera]

This is something you should cover in your prematch.

I would discreetly, then less and less discreetly, keep trying to get your partner's attention during the rally. I would be inclined to let the rally play out, then ask the R1 to invite me over to share information.

Though you are certain a fault occurred, this is something that is ultimately the R1's final decision, and not something you want to run the risk of getting into trouble calling yourself as R2.

You did the right thing in trying to get the call right, but you want to make sure your partner has every opportunity to look at you and make that call first.