I have an issue with creating my invoice, and keep getting this error  "message":"JSON is not well formed". What is wrong with my JSON string?

'{"notes": "Thanks for your business.", "discount": , "discount_type": "entity_level", "is_inclusive_tax": false, "due_date": "2017-05-31", "line_items": [{"description": , "item_id": "132685000001781697", "discount": , "rate": 10, "name": "Storage & Scanning", "quantity": 4, "item_order": 1, "tax_id": , "unit": }], "payment_options": {"payment_gateways": [{"additional_field1": "standard", "gateway_name": "paypal"}, {"additional_field1": "", "gateway_name": "stripe"}]}, "terms": "Terms and conditions apply.", "allow_partial_payments": true, "payment_terms_label": , "customer_id": "132685000000041027", "date": "2017-05-31", "Customer": "Elson", "is_discount_before_tax": true}'