You can make existing cart price rules customer specific and also create new cart rules.

To enable the customer specific discount to any rule, select any rule you want to make customer specific.

You can edit the selected rule and set the Customer Specific field to ‘Yes’.

[NOTE: when you enable customer specific to yes, then the customer group field will be disabled.]

After enabling the customer specific field you can see a separate custom tab called ‘Customers’ below.

In that tab you can see the customer grid. In the grid you can see the customer list with the filters.

You can select single or multiple customers to whom that particular rule will be applied.

Only selected customers are eligible to get that discount.

After that save the rule.

After creating a rule based on customer specific you can see the Customer Specific column in the cart price rule grid.

GraphQL Mutation and Rest API are of default Magento. Our extension work with this Mutation and API of default Magento.

If the coupon code is customer-specific then only selected customers can access that coupon code.

mutation {
  applyCouponToCart(
    input: {
      cart_id: "rUSKBXj0oM13XCsd61foEpnauQZ8Pkk7"
      coupon_code: "H20"
    }
  ) {
    cart {
      applied_coupons {
        code
      }
    }
  }
}

Request URL:

yourdomain.com/rest/V1/carts/mine/coupons/H20