Storefront api Cart item is null!

[hates]

Hello,

I want to sync our customer's website cart and mobile app's cart. For example customer logins from website and adds 2 items to cart tehn left it. After that customer opens the mobile app, I want to show dialog "you have added 2 items before, Do you want to add these items your cart?"

For this purpose, I will save all carts changes to our backend and I managed to listen carts/create and carts/update webhook. I can receive carts changes immediately, but when I use the storefront API to retrive a cart to detect cart belongs which customer, api is returning cart is null.

{"data":{"cart":null}}