@DJW . . .
https://www.agl.com.au/residential/solar-and-batteries/virtual-power-plant
Down the bottom in the things you should know compatible batteries and inverters.
Yes the above link is for VPP, but just t ocheck about the usual compatibility of the Sungrow inverters / batteries.
There are even less strigent requirements that come up when you bring up the Battery Rewards page . . .
https://www.agl.com.au/residential/energy/compare-plans/energy-offer?webid=BRPLAN
In the elegibility criteria "Have a solar battery of any brand installed at the supply address"
Have you spoken to anyone at AGL, beyond the support front line ?
They can sometimes be limited in their knowlege base.
Maybe a tech dept type can assist more.