-walletnotify mechanism is used with Bitcoin-like RPC wallets to notify the plugin that an incoming deposit exists.
The plugin does not distribute POS dividents to users, therefore there is no “stake” category for transactions. Any stake earnings are added to the hot wallet balance of the site, not to any user balance.
In the future there might be a divident-paying plugin extension, but this is not implemented yet.
If you would like to be notified of stake rewards from your wallet, you will probably have to find another way. Having said this, maybe you could implement your own code that binds to the
action_wallets_notify_wallet action. This will receive transaction IDs. You can then check if these correspond to transactions that are POS rewards using some online service or via communication to a wallet. But this something out of scope of the plugin.