Hello, I had lots of issues at first with t-shirt prints. After lots of trial and errors, I found out that in my case I needed to print the zap code on the correct contrast color. This meaning, if the zap code was black and had a white background when created, then I had to use the same set up… a black zap code with white background. I solved this issue by printing on white t-shirts and also by having the screen printer print a white background for where the zap code would be printed on top of on colored t-shirts. I am sure there may be another way to achieve this, but this was my solution. I hope this helps. Best, Michael