

Subfloor prep advice for small guest toilet (with unusual base)
Hi everyone,
We’re in the middle of a laundry reno and have just finished removing the old tiles. The laundry itself has a solid concrete floor, so we're ready to tile there. But in the adjoining small guest toilet, things are a bit odd.
Near the toilet flange, it looks like the previous builder used loose soil or rubble as a fill, then smothered it with adhesive to try and level it out. We're planning to lay 600x1200mm tiles, so we want to get the subfloor right before going any further.
Has anyone come across this kind of setup before?
What would be the right way to prepare and level the floor before tiling in this case?

Appreciate any tips or product recommendations!
Want me to tailor it more toward DIYers or trades, or keep it balanced like this?