Shopify GraphQL draftOrderCreate error: "Applied discount value can have at most 2 digits after decimal point" — but value is correctly formatted

GraphQL Admin API Troubleshooting
1

Hi Shopify Community,

I’m encountering an issue with the draftOrderCreate GraphQL mutation when applying a fixed amount discount to a line item. Despite formatting the appliedDiscount.value field to exactly two decimal places, the mutation consistently fails with this error:

Error: Applied discount value can have at most 2 digits after decimal point
Field Path: lineItems[0].appliedDiscount.value

We’re building a custom integration to programmatically create draft orders with a fixed amount discount applied per line item. Here’s a simplified example of the mutation payload we’re sending:

{
  "variantId": "gid://shopify/ProductVariant/49974694904086",
  "quantity": 3,
  "appliedDiscount": {
    "amount": "42.65",
    "description": "TFM Price Difference",
    "value": 42.65,
    "valueType": "FIXED_AMOUNT",
    "title": "TFM Discount"
  }
}

What We’ve Tried
Used decimal.Decimal in Python to calculate and round the discount value precisely to 2 decimal places (Decimal(‘0.01’) with ROUND_HALF_UP).

Verified the payload is being serialized correctly with custom JSON encoding (e.g., 42.65 is not turning into 42.650000000000006).

Removed amount field to see if there was a conflict — still the same error.

Manually tested mutation using Shopify’s GraphiQL admin app with the same input — still fails.

Tried with smaller values (e.g., 1.00) — still fails.

Questions
Is this a known issue or limitation in the DraftOrder API?

Are there undocumented constraints or formatting expectations for appliedDiscount.value?

Should we be using a different data type or approach to ensure compliance with Shopify’s backend validation?

2

I don’t use this exact API but can you pass the value as a string?