I was creating code at google scripts https://goo.gl/pKUc7D to test order / invoice reciept markup from Google's own documentation at https://developers.google.com/gmail/markup/reference/order
It did not work. I could be missing something? The structured data testing tool gave me green checks for everything in the script textarea. I'm going to github the results to share with anyone else who runs whmcs billing software.
I'm not familiar with WHMCS billing software and how it works. I checked out your sample and I was a little confused. I see you're using:
This isn't supported in Gmail/Inbox. You'll have to follow the microdata example(s) for Order on the documentation. I noticed that even though your markup checks out with the Email Markup Tester, it doesn't mean it will be supported.
I extracted the details from your sample data and created an example for you.
This will trigger a View Order button that will direct your customer to the "invoice/receipt." Also note, I used the discount property, which I noticed in your microdata, the discount was being recognized as an item purchased.
Oh, also, if you're trying to send a bill, set the orderStatus as:
I hope this helps.