To obtain your invoice for a Sony LIV subscription, you can follow these steps:

For subscriptions made directly through Sony LIV:

Log in to your Sony LIV account.
Navigate to the "My Purchases" section.
Here, you should find a list of your subscriptions along with options to view or download invoices.
 

For subscriptions made via app stores (e.g., Google Play Store, Apple iTunes Store, Amazon Store):

Access your account on the respective platform. 
Navigate to your subscriptions or purchase history.
Locate your Sony LIV subscription and download the invoice from there.