Welcome to the Bunnings Workshop community. It's fabulous to have you join us and thank you for sharing your question about the pebble resurfacer.
I've just contacted our provider of Max Pro pebble resurfaced mix. They've informed me that the Max Pro can be applied vertically however, you'll need to use a compatible tile adhesive. Unfortunately, Max Pro has been discontinued by Bunnings along with its associated products which include the vertical adhesive.
I suggest speaking to a tiling specialist who has experience with using Max Pro and asking them their opinion on possible compatible adhesives. My only other recommendation to change the surface of the brick wall is to render it. This will give it a nice uniform finish and will be easier to maintain than a pebble surface wall.
If you need further assistance, please let us know.