Aeroquip 816 ( different than AN816) is a cutter style hose end. The tapered section around the stem actually traps a thin wall of the rubber liner as it cuts into the hose. This seals the hose to the stem when the fitting tightens up.
Take the collar and turn it 1/4 loose so the hose sits slightly lower in the collar. LUBE the hose so the cutter section can 'slice' the hose. Tighten it up.
One issue on 'reusing' a 816 'reusable' hose end is digging out the out section of hose thats now trapped inside the cavity between the stem and the cutter section. if you dont remove it, it will not seal, and you may NOT be able to reinstall the fitting. If its a used fitting, check that.
Tom