CheckoutCreate mutation lineItems INVALID id error

[beelaineo]

I refactored my headless app using the Storefront API, to create a new checkout whenever a user changes their country, to return localized prices.

Whenever I have a checkout with pre-existing items in the cart (lineItems) and I include those lineItems in a CheckoutCreate mutation, Shopify Storefront API responds with a code: "INVALID" error on the lineItem's variantId.

The response is not returning any helpful information, beyond a general link to https://shopify.dev/api/usage/versioning#deprecation-practices

General Headers:

Response Headers:

Payload:

mutation CheckoutCreate( 
    $email: String
    $lineItems: [CheckoutLineItemInput!]
    $shippingAddress: MailingAddressInput
    $note: String
    $customAttributes: [AttributeInput!]
    $allowPartialAddresses: Boolean
    $countryCode: CountryCode!
  ) @inContext(country: $countryCode) {
    checkoutCreate(
      input: {
        buyerIdentity: { countryCode: $countryCode }
        email: $email
        lineItems: $lineItems
        shippingAddress: $shippingAddress
        note: $note
        customAttributes: $customAttributes
        allowPartialAddresses: $allowPartialAddresses
      }
    ) {
      checkoutUserErrors {
        __typename
        code
        field
      }
      checkout
    }
  }

Payload Variables:

{
    "lineItems": [
        {
            "variantId": "gid://shopify/ProductVariant/316533997568980",
            "quantity": 1
        }
    ],
    "countryCode": "DE"
}

Response:

{
    "data": {
        "checkoutCreate": {
            "checkoutUserErrors": [
                {
                    "__typename": "CheckoutUserError",
                    "code": "INVALID",
                    "field": [
                        "input",
                        "lineItems",
                        "0",
                        "variantId"
                     ]
                 }
             ],
             "checkout": null
          }
      },
    "extensions": {
        "context": {
            "country": "DE",
            "language": "EN"
         }
     }
}