How to Add 10% Discount ONLY IF Total Order Amount is greater than £12?

Hello everyone

I have recently installed Samba POS v3 and have been intensely reading the forum.

I have managed to do all what I need in order for the system to work.

However, I am unable to do the following; 

Add 10% Discount ONLY IF Total Order Amount is greater than £12

I have added the 10% and is working but this applies in all instances. How do I get this to only apply for order values of more than £12?

I would really appreciate your help.

Thanks