There is a problem in LoRa App Server integration.
For HTTP, REST and gRPC, there is no join notification post request until an uplink happens, Then both join and uplink notification post requests are send to destination URL.
For my applications it is really important to receive join notification and this seems to be a simple problem to solve!
This is by design. Only on the first uplink it is known if the device has successfully (re)joined the network. See https://forum.loraserver.io/search?q=join%20notification.