ColbyFlanagan
Maybe send a .yml instead? there could be spacing issues that aren't seen because of the formating. Or use this feature.

And also @KkwetPistache is correct, you'd need to make the modifier for the leg slot instead, thanks KkwetPistache!
Example of a boot item!
enderite_boots:
display_name: Enderite Boots
permission: secret
resource:
generate: true
textures:
- armor/enderite_armor/boots
durability:
max_custom_durability: 550
specific_properties:
armor:
slot: FEET
custom_armor: enderite_armor
attribute_modifiers:
feet:
armor: 4
armorToughness: 3
events:
wear:
potion_effect:
type: SPEED
amplifier: 2
duration: 99999
unwear:
remove_potion_effect:
type: SPEED