Does fasting become invalid upon tasting the flavor of juice remaining in the throat after Fajr, while swallowing saliva, despite having rinsed the mouth before the Adhan of Fajr?

Smoking electronic cigarettes is haram, and one must repent from it. As for the taste that a fasting person finds in their throat from smoking, it does not invalidate the fast by itself, because nothing has descended, and a mere taste does not break the fast.