There is not actual pause button, but there are hotkeys you can use to start and stop the bot. For all intents and purposes it acts virtually like a pause button, with the only downside being that after stopping and start the bot, the bot will have to re-cache your stash. Not a big issue imo.
I dont know what the default keybinds are, something like control + s or something along those lines. You can open up the SETTINGS > GLOBAL > GlobalSettings.json file (with notepad) and remap the hotkeys.
Example: If you want to start and stop the bot with F1, then set: