After greeting, I want to send the number of allowed users attending the current meeting in options i use api frame .
If I understand correctly, you want to dynamically set max number of occupants per room?
This is not something you can currently set using IFrame API and has to be done from a prosody plugin. This will require you to have your own deployment (not meet.jit.si), and some additional dev work since the provided mod_muc_max_occupants.lua in a standard setup works with a fixed number of max occupants.
There are some possible options to achieve per-room limits discussed in the following thread:
Perhaps if you can use the information shared by @shawn and expose a http call through your custom module you can set limit to module dynamically over http/https. Just thinking…
i use iframe but i make solution its worked for me first i make var named allowedCountMembers and asign 3 for it
next step i use api function getNumberOfParticipants() when user joined meeting i get the actule count now and make small check if getNumberOfParticipants() > allowedCountMembers i use window.location to my spacific url i hope its can help any one use iframe method