How can I request the invoice for my purchased subscription?

That depends on where you bought your subscription:

Google Play Store

This is how you request the invoice from Google: https://support.google.com/paymentscenter/answer/7520537?hl=en

Apple App Store

Please contact Apple support directly at https://getsupport.apple.com

7Mind Homepage

• When you bought a subscription via FastSpring (before 20.01.2022), you received a confirmation email from FastSpring right after ordering. It includes a link to FastSpring where you can download your invoice. If you no longer have this email, send a message to our customer support with your 7Mind profile email address so that we can request the invoice for you.
• When you bought a subscription via Chargebee (after 20.01.2022), you are not yet able to manage it on your own. Please send us a message to our customer support with your 7Mind profile email address so that we can request the invoice for you.

• Subscriptions purchased after 20.01.2022 will be processed via our new payment provider Chargebee. After completing your order, you will have received a confirmation email with your invoice. If you no longer have this email, you can access the customer portal via this link, where you can manage your subscription and download your invoice. If you have any questions or difficulties, just send us a message to our customer support with your 7Mind profile email address.