@Vincent-TP thank you for your quick response.

lets consider er8411 can handle for 800 clients. but my current setup it can only accommodate 260 clients. after that the clients cant access the portal

I already did dividing it in multiple vlans in networks switch

what do you mean multiple separate networks?

adding other L2 switch? 

  @cgmedina 

Your issue seems related to your OC300. Portal are picking up from controllers. Your OC300 is too busy handling all data pollings of all devices while also providing portals for web authentication. If you enable DPI in your gateway this increase more load to you controller. I dont see issue on your vlan setup and specially you place your management in different vlan which is more scalable.

You should check the OC300 resources.

  @Vincent-TP 

Hi, my main goal is to ensure that all clients are on the same network—meaning both voucher users and local users should be able to connect seamlessly. This way, if a voucher or local user moves to another building, they can still use their access without any issues.
Your recommendation works quite well. However, when users are assigned to different sites with separate gateways, voucher and local users can't use their credentials across buildings, which defeats the purpose of a unified network.
I’m surprised that such a high-end device like the ER8411 and OC300 combo limits voucher users to just 256. Meanwhile, the OC300 datasheet claims it supports up to 50,000 local users.  =)

By the way it took me a while to rely to you post because i have tried 4  SSID and 4 site 

  @Wifi-freak 

I also tried your suggestion to enable DPI. It improved the OC300’s performance, but it reduced the client capacity by half. The OC300 now supports 5,000 clients, but the hotspot feature-still only handles up to 256 clients.

I believe the hotspot feature itself has a built-in limitation. I waited several days before replying because I’ve been experimenting with different setups to improve my current network infrastructure.