This is a glyphosate product that is supposed to kill any plant it touches. Whether it will "damage" the plants on the other side ot that wall depends on it any of it drifts there.
There are better, more environmentally safer, methods of controlling unwanted plant growth.

Were you invited/permitted to put chemicals on someone else's property?

Emma, this is a product you really need to be very careful of in most residential settings.

It's a bigger problem being moved by watering or rain to areas downhill from where its been applied, not up hill. But its not advised to use it withing two times the distance of the canopy of trees or shrubs, so if you have a neighbor with shrubs for example that are 4' wide, you'd want to stay at least twice that far from them and not apply the product any closer than 8' away (per the label) even if you were putting it down on ground inside your ownership boundary.

It's one I don't find appropriate many times for a lot of different reasons, there are less problematic products you can use with less risk for inadvertent damage. To your own things, or to your neighbors :) Your climate should be somewhat similar to my own and it doesn't last a year here after application anyway, it's effectiveness is much shorter period than that with my persistent coastal rains. If you'd have to reapply anyway, you may as well find a less toxic product to give your attention to.

Thank you morz8 for your ADVICE, which was what I was hoping for, rather than the sarcasm posted by other members. I have used a rootkill weedkiller. Your help is much appreciated.

Not sarcasm, an honest question. I see nothing sarcastic about the info Kim provided either. A "small area of weeds" should be easy to clear manually, but kudos to you for asking for advice regarding using chemicals if that is the method you prefer. Glad you found what you were looking for. Best of luck and results!