since shopify's transaction reporting is broken, I'm trying to use the API to get transaction fees for orders and basic accounting. In their API docs, they have their endpoints and parameters listed for getting/posting transactions. To "Receive a list of all Transactions", the docs say
Transactions belong to an order. So the ID you are wondering about is for one specific order. So if you want transactions for your accounting system, the important thing you're basing your API work on will be orders. So setup your code to first off download the orders of interest. Say for a month. Now for each order ask for the transactions, and produce your report.