My custom trigger icon does not appear on the Size Guide button
The button can show only one icon mode at a time (ruler, shirt, scissors, or custom).
Steps to fix
Open Templates → Trigger Button.
In Show Icon, click the image/custom icon option.
Upload your icon (SVG/PNG recommended).
Confirm a preview appears in the custom icon row.
If it still shows a default icon, click the custom icon button again to force icon mode back to custom.

