Setup btcpayserver-docker with the opt-add-ltcmweb
fragment.
Install the plugin (or restart BTCPayServer if already installed).
Add MWEB View Keys to Litecoin MWEB Wallet settings in BTCPayServer admin.
They can be retrieved using Electrum MWEB (release-9 and later).
Yep. The first one is the scan key, the second the spend pubkey. Only the first is needed to detect payments, but both are required to generate addresses.