What variable to use to substitute the URL of the box in the form: https://url_my_onebox/...

It looks like there used to be a very useful variable like this, but I can't find a reference to it anywhere. I remember that Maksym Tyndyk made it. Aiming to send a link to the app/task in your box via message: - email - telegram - viber - SMS, etc The message must be in the form: https://url_my_onebox/ may be a link to an application in the box, to a task, etc Here are some examples of such links, which we create thanks to the variable to OUR box, from where we send messages: https://url_my_onebox/app/contact/ https://url_my_onebox/app/crm/ https://url_my_onebox/app/automatization/ That is, the variable should default to a reference to the box in which the message is generated: https://url_my_onebox/ Please tell me which variable should be used for this?