How to make JSON order counter?

Question

PHP

When paying, you need to specify the order ID, all information about the product is stored in a JSON file (name, price), you need to make a product counter so that the ID increases by 1 with each purchase, i.e. first id = 1, bought the product (php file worked) and id became 2 and so on

Answer 1

ID is not necessarily auto-increment, use for example UUID

Answer 2

read, json_decode, add, json_encode, write.