Issue with GraphQL mutation command in JSON format

Dear Experts,

When I am sending GraphQL Mutation command as following JSON format it is shown following error, but when sending Query and Variable separately it is working good. Could you pls help what’s wrong in the JSON format.

Variable $input of type ProductVariantInput! was provided invalid value

Payload as JSON:

{
"query":"mutation($input:ProductVariantInput!){productVariantUpdate(input:$input){productVariant{id sku inventoryItem {id sku}}}}"
,"variables":{
"id":"gid://shopify/ProductVariant/123456"
,"sku": null
}
}

The following Command executed successfully:

Query:

mutation ($input: ProductVariantInput!) {
    productVariantUpdate(input: $input) {
        productVariant {
            id
            sku
            inventoryItem {
                id
                sku
            }
        }
    }
}

Variable:

{
    "input": {
        "id": "gid://shopify/ProductVariant/123456",
        "sku": null

    }
}

Thank You,

Kamal Hossain

I resolved it by adding Input object…it was missing in the variable

{
"query":"mutation($input: ProductVariantInput!){productVariantUpdate(input: $input){productVariant{id sku inventoryItem {id sku}}}}"
,"variables":{"input":{

"id":"gid://shopify/ProductVariant/32150580527153"
,"sku": null
}
}
}

Thank you.