The webhooks will have the transaction id in the payload. To get the complete transaction details you will have to use the getTransactionDetails() method call, which has been hyperlinked in my previous post. To do that without installing composer is doing it the long way around. You will need the php sdk. The dependencies will have to be installed somehow, and composer is the easy way to do it. It is automatic.
To set up a webhooks endpoint just create a file on your remote server and then put that url on your merchant interface. On the file you want to capture the Json content, which is the payload that contains the transaction Id and a limited amount of other data about the transaction. I unfortunately cannot give you sample code because I am on my phone at a restaurant. It is very simple and only takes a few lines to capture the payload.
But I suggest that you get the php sdk and composer ASAP. Both are free and there is a LOT you can do with the sdk package once installed that is very useful. If you have questions about composer or get stuck post them on here. I and others here will be able to help you.
