You can use the default OctoPrint API to send the same commands configured in the plugin settings.

Thanks a lot for the message. What is the command to send to run "Update Mesh Now" like the button in the application ?

Literally what I just said. It does a send Command as if from the control tab of all the lines configured in the plugin's setting. There is no direct API to do the same thing. There is a custom action handler though, where if your printers support it you can use the action BEDLEVELVISUALIZER_LEVELBED.

https://marlinfw.org/docs/gcode/M118.html

So you could use the OctoPrint API to send the single M118 command.

For clarity, the full command would be M118 A1 action:BEDLEVELVISUALIZER_LEVELBED. Test that from the terminal tab and see if anything is returned. If it is not, then your printer doesn't support HOST_ACTION_COMMANDS.

thanks a lot. now we realized that our Prusa Mk3 doesn't support M118 commands. Sorry. i have to do the bedlevel manually so.
Thanks again

I've added an API POST command to start the leveling process remotely. It's available in 1.1.2rc5 version, you can change the release channel in OctoPrint's Software Update settings to Release Candidate for the plugin and update when prompted.

URL = http://octopi.local/api/plugin/bedlevelvisualizer
PAYLOAD = {"command": "startProcessing"}

great !! thanks a lot. you save me !