Instamatic cameras take the 126 film format which is discontinued. I opened an empty 126 cartridge and rolled some 35mm film with the backing paper.
The 155X camera has only two settings, sunny and cloudy, so good light is required.
The film is advanced with a special procedure. Pressing the shutter button advance the lever one or two times, release the shutter button, then advance the lever a bit more until the shutter is cocked.
I found out that the two and half frame advance leaves a lot of blank space, one and a half advance is about right, sometimes too tight. You can always check the frame numbers on the backing paper.
The results