[Closed] Thompson Covert does not work out of the box,... Advice?

Just before I send this dropper back to Stif cycles for return to Thompson has anybody had a similar problem 'straight out of the box' to this..... Seat Post arrived at full extension, set up as per instructions and the cable is nice and tight, the 'pull' on the bottom of the actuator is correct (full movement and return on release) but the post remains locked in full extension with zero movement. Does the post need charging with air? Is there something I can try before accepting it is just a duff post and send it back? Cheers.