Down to zero

Cock the gun then fill the gun normally as you always always do then dry fire once.

Remove the stock. Take notice any hissing sound out of the shroud and front filler Ares and manometer underneath the gun.

Use 2 balloons or condoms (clean ones of course) use rubber bands and tie one to the end of the barrel and the other over the male Foster fill over the black metal cylinder. If it's the regulated version over the manometer and quick fill holes where the probe plugs in. Spray soapy water around manometer area notice any bubbles?

If the balloon over the barrel end fills up that's your worst case scenario your valve seat is leaking. All other leaks should be simple to DIY... You could shoot it like normal to see if it fixes itself if there was only dust or debris in the valve seat or a sticky check valve.

Note if still under warranty If you are the original owner you could send it in after calling to verify if it's covered.