You will receive your subscription purchase receipt on the Apple App Store / Google Play Store email that you use while purchasing Innergy. The receipt should look like this:

Receipt from Apple (for iOS users)

Receipt from Google (for Android users)

In case you did not receive the purchase receipts from Apple/Google on email, you can view it by referring to one of the below mentioned links. 
 
Apple: https://support.apple.com/en-us/HT202039 

Google: https://support.google.com/googleplay/answer/2850369?hl=en