I placed river splines and now cannot paint foliage on my landscape

I placed river splines from the procedural nature pack and now cannot paint/remove foliage on my landscape. I can paint foliage on the river splines but not the landscape (i can place foliage on 2 other smaller cave landscapes within the level).

I’m very new to this so im sure i’ve missed something and any help would be very much appreciated.

I’ve tried looking for an answer online but to no avail.