its very easy to check
pump it up to pressure, check the extender tip if air is coming out
(wet finders with soap and seal the opening) if no air is coming out
then there is still a slight possibility of air escaping from the joint
(but very unlikely).

In that case your tire may have a puncture. How fast is air leaking
?????

If the air was coming from valve you may have bent the screw valve or
the rubber ring inside is bad or something is preventing it from
closing all the way. remove the tire and check. Dont throw the tufos
away you can fix the valve if the core is removable. after repair a a
tad of grease to the valve before you add the extender and use a pair
of pliers to tigthen them dont crush it).