We are developing a custom app through that app we are trying to import products with API. We have a product that has two options which are size and color and there are 72 product variants. And every variant has its own picture. So in short one product has 72 variants and 16 pictures. While we are trying to create product with API we are having an issue "Server error: POST https://shop.myshopify.com/admin/api/graphql.json resulted in a 502 Bad Gateway response:" How can we solve this problem? And why are we getting this?