Hi,
Even if you use auto park, your MPK should match order of Monitored Call Park - park+*5901, park+*5902 and so on. It is better if you just let them answer the call from RG and place them on park.
I have several dozens of medical offices and pizza places, that is what they all do. They just say: "Please hold" and place them there and return to original call.
That is how they were used to on Nortel side. To them it is "placing on hold" and they do not understand what is "park call" or the Device "Hold". I have the MPK label on many set as "Line 1", "Line 2" and so on because that is how they were used to. Asking where is my Line 6! Why my Line 2 isn't ringing, and so on.
Agent login is done on FusionPBX side. You create an Agent and you can set what status it will automatically have. In your case Logged In.
They technically do not need to even know they are agents. Rebooting the Phone won't change the status of an Agent. It doesn't dictate what is happening on the Server side, it just is an intermediator. Restarting Call Centre, Services or rebooting the server will.
The Call Centre monitoring callcenter+[queue_ext] will change status when a call is waiting, but they will not be able to pick it up until original call is released.
Some places prefer to get a second call, some do not. You adjust on however they feel is better for them.
Most come from Nortel/Norstar environment and they wouldn't even know what we are telling them.
I also avoid using Line Mode and use Account Mode (Settings - Programmable Keys - Key Mode: Account Mode P8369=2) on the Phones. Gives more space for MPK's. If you use GXP2140 and have it as Line Mode and need to put two park calls and a page, Line mode can cause issues. I hope you are using GDMS for Grandstream, even if you provision via FusionPBX as it serves as RPS manager and advanced troubleshooting tool rather than GAPS or Device Logs. It is also better to upgrade from there than FTP or HTTP/HTTPS server side.
There is also a status notify if you use DP Series and some schmuck places the HS in DnD and complains about no calls coming in. It might not even notify server of DnD status unless config files are properly done. Mine are heavily modified.
Ok, I'm done with a Novel here. Enjoy