If enable in config "allowAutoCurvingRecipes" curving press can have auto added recepie with multiple input items example "3 Iron Ingot to Bucket"

If added manually this is not working:
{ "type": "vintageimprovements:curving", "mode": 1, "ingredients": [ { "item": "minecraft:iron_ingot" }, { "item": "minecraft:iron_ingot" }, { "item": "minecraft:iron_ingot" } ], "results": [ { "item": "minecraft:bucket" } ] }

Fixed