On LiqPay start page enter your phone number (used as login) and wait for SMS with code. Enter that code. You’ll be redirected to personal cabinet.
On main screen click on Settings in control panel on the left.
Choose API option in settings. System will provide you with two keys: public and private. Click on eye icon to see private key. Copy this keys.
Copied keys paste in relevant fields in mssg.me service.
Tip: You can enable test mode in LiqPay personal cabinet and use test keys in mssg.me service to test integration.