Jiwa

which code section should I use in the plugin to do something when the Jiwa is started?

I have to push the data on an online store for one time only.

I'd add a handler inside the ApplicationManagerPlugin.Setup method and do it there - putting a condition on which user this runs as in case other users login at the same time and triggers your code by mistake:

Usually for sending data to an external system I've usually used a scheduled plugin, which means using scheduled plugin service you can have the same code and run it once or even multiple times if needed as the schedule will determine how often it runs.

Mike's option however is best choice if anything is user specific.