There are many different ways to fix a broken nail. You can use acrylic or gel, but they are not flexible enough. Especially if the client wants to "save" the length of the natural nail. Polygel is a good solution here. It is strong enough to fix it and flexible enough to stay on for a long time.
I tried Polygel to fix the crack and after 3 weeks I still don't have any problems. No chipping, no lifting. I hope this method will work for you and your clients too.