What is wrong with my enchantment?

It is supposed to add more knockback when crouching, but apparently it does nothing... { "description": "Crouch-Knockback", "supported_items": "minecraft:diamond_sword", "slots": ["mainhand"], "weight": 100, "anvil_cost": 0, "min_cost": { "base": 1, "per_level_above_first": 0 }, "max_cost": { "base": 10, "per_level_above_first": 0 }, "max_level": 3, "effects": { "minecraft:knockback": [{ "effect": { "type": "minecraft:add", "value": { "type": "linear", "base": 30, "per_level_above_first": 200 } }, "requirements": { "condition": "entity_properties", "entity": "this", "predicate": { "flags": { "is_sneaking": true }} } }] } }