Tested with Magento CE version:
2.1.0 - 2.4.5
Download the plugin's zip archive and move its contents to the root directory of Magento using a method of your preference, such as FTP or SFTP.
php bin/magento setup:upgrade
php bin/magento setup:static-content:deploy xx_XX,
Log in to the Magento administration panel and go to Store -> Configuration -> Sales -> Payment Methods -> OPAY Payment Gateway.
Fill in the mandatory settings for the OPAY plugin and click on Save Config. If your online store is not registered with the OPAY system, fill out the registration form and receive all the necessary data for the settings.
php bin/magento cache:clean
Using the Magento admin panel go to System -> Cache Management and click on Flush Magento Cache.