Currently the plugin is available for the manual installation in the Releases due to some technical problems in the BTCPay Plugins Builder. The old version (1.2.1) displayed in the BTCPay Plugins Manager is not compatible with the BTCPay v2.1.5!

Usually, the plugin is available in the BTCPay Plugins Manager. To display it in BTCPay, click in the left menu on "Manage Plugins" you will see the plugin in the list, click "Install" to install it.

When done, restart your BTCPay Server... You will find the "OpenSimulator" link add to the Plugins list in the left menu. The docu is in the repo Wiki...

Note: I am not affiliated or work with/for Opensimulator , BTCPay, NSL... I just add my magic touch where i feel it is necessary for the common good.

Enjoy :)