updating inventory quantity with PUT returns error - shopify

Question

Here is the body
{
"product": {
"id": 1202316036,
"title": "cricket bat for sale",
"variants":[
{
"inventory_quantity": 500
}
]
}
}
This returns the following error
{
"errors": {
"base": [
"The variant 'Default Title' already exists."
]
}
}
But where as the updating the title seems to be working fine. Here is the body
{
"product": {
"id": 1202316036,
"title": "cricket bat for sale"
}
}
I am sure that PUT header(Content-Type: application/json) are set properly. Because updating title does work. How should I go about updating inventory management
ps: I am using POSTMAN for using shopify API

Answer 1

So you do need the variant id otherwise Shopify thinks you are creating a new variant. Also your variants need to have been set up for Shopify to manage their inventory. e.g.
var product = {
product:{
id: productId,
variants: [
{
id:5991257025,
inventory_management : "shopify",
inventory_quantity:20
},
{
id:5991257089,
inventory_management : "shopify",
inventory_quantity:26
}
]
}
};

Answer 2

I'm not sure if you can do multiple variants per call but to update a single variant's inventory quantity you'd do it like:
var payload = JSON.stringify({
variant: {
id: variantId,
inventory_quantity: qty
}
});
and then put that to "https://myshopifydomain/admin/variants/" +variantId + ".json";
possibly all you need to do is add the variant id for each variant you are updating. Your variant ids can be gotten by GETting the json for your items.