Sewing with Metallic thread can be a challenge. I have some successful customers that are willing to share how they make it work.
Reoccurring question from new embroider:
The result is that you hoop your clothing item, which stretches the cloth, and you sew with the metallic thread which is stretched also. There ends up a lot of tension on your design. When you un-hoop the design the clothing puckers and gets worse with each washing.
How to solve the issue...
Try these and let me know if these help and/or you find something better.