Thank @c10s for support.  I have solved this problem.But I have another problem that I don't know how to change product price from webhook before switching to checkout (For example, I want to add a free gift cart product to checkout but with the cond...

@hassain Can you help me with this problem? Thank you.

I am researching to develop an app on shopify. I've used "mutation"And get the return result: 'Field \'checkoutLineItemsAdd\' doesn\'t exist on type \'Mutation\''Would you please tell me why not? I am using https://github.com/osiset/laravel-shopify t...