Shopify GraphQL Mutation Doesn't Work In CURL Or Postman But Does With GraphiQL App

Question

When I'm using the following mutation in GraphiQL App it works perfectly but when I run it using Postman or CURL it just doesn't work. This issue is happening for Function related mutations only.

The Mutation:

mutation {
    discountAutomaticAppCreate(
      automaticAppDiscount: {
        title: "Volume Discount Created from APP 011", 
        functionId: "9d8aas8-78asd-8d7sa-86f0-dg789asdfa9sd", 
        startsAt: "2023-09-19T00:00:00"}
    ) {
      
          # Payload
          userErrors {
              code
              field
              message
          }
          automaticAppDiscount {
              discountId
              title
              status
              createdAt
              endsAt
          }
      
    }
  }

The error that I get when using CURL or Postman:

"data": {
    "discountAutomaticAppCreate": {
        "userErrors": [
            {
                "code": "INVALID",
                "field": [
                    "automaticAppDiscount",
                    "functionId"
                ],
                "message": "Function not found."
            }
        ],
        "automaticAppDiscount": null
    }
}

The Functions that I'm using to make the CURL request(Though it's not that important as this is just working fine for many other queries):

public function makeGraphqlApiRequest($data)
{
    $storeName = 'store-name';
    $apiVersion = '2023-07';
    $accessToken = 'access-token';

    $graphqlEndpoint = "https://$storeName.myshopify.com/admin/api/$apiVersion/graphql.json";
    
    $headers = [
        "Content-Type: application/json",
        "X-Shopify-Access-Token: $accessToken"
    ];
    
    $ch = curl_init();
    
    curl_setopt($ch, CURLOPT_URL, $graphqlEndpoint);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    
    $response = curl_exec($ch);
    
    if (curl_errno($ch)) {
        return 'Curl error: ' . curl_error($ch);
    }
    
    curl_close($ch);
    
    return $response;
}
// End makeGraphqlApiRequest Method

Later I rechecked the "shop-name" and "api-version" both in GraphiQL and CURL, Postman. They all had same shop-name and api-version. What can I do to solve the problem? Thanks!