Light Weight #2 Invisible
Invisible Zippers come in many different sizes or gauges.
I have stocked
#3 or #4(3.8mm),
#5 or #6 (5.8mm)
This is the gauge or size invisible zipper that will fit in your little plastic foot. I drive an old Bernina 950 & that metal foot will fit both the #2 & the #3/4 sizes. If you have a small welt foot, that will also work. Or just stitch in the ditch.
These are exceptional quality zippers! However, invisible zippers are never as strong as a standard coil zipper. Your zipper might have popped because of stress on it. In that case, you might try a Medium Weight Invisible (a little heavier & harder to pop) or a Standard Coil #3 zipper (what we used to call a "dress" zipper) as a replacement.
Because the #3/4 works so much better, I will discontinue the #2's over 2023. Hence, why they are on sale.