Drones, though last week they claimed they'd stopped supplying them, even though previously they'd denied supplying them. There is significant opposition in Iran to the supply of drones to Russia because their mantra has always been neither east not west and that opposition from hardline clerics has become very vocal in recent weeks.
It does seem like the Russians have almost run out of Iranian drones, there hasn't been much talk of them recently. Multiple reasons, Ukraine are very good at shooting them down now, Russia were having to send them in swarms of 10-15. Irans capacity to make them is only 150 per week