Why is the zip curved after stitching continuous zip chain to the garment?
Spiral/coil zips have an S twist and Z twist in the teeth creating a “smile” or “frown” appearance when the teeth are joined. The left and right teeth should be both in the same direction/condition. If this is not the problem check the sewing tension is equal on both sides of the zip.
How do I stop the teeth creating an impression on the front of the garment’s fly panel?
Change the zip for reversed coil type zip and slider.
Why is the chain/teeth opening behind the slider?
Bottom stop should be protected with a bar tack to prevent direct strain on the zip. If bar tack is fitted but breakage still happens, check effective opening of the garment. Try garment on model or dummy to see possible causes of the breakage.