I am having problems getting a new mailbox to work correctly on our Strata system.

Phone is programmed to forward calls to XXX which is our voicemail extension. It gives "that is an invalid entry" after ringing the right phone.

I've noticed some of our phones are programmed to forward to XXXV and I have no idea how you program the V part. Have also noticed that most extensions in the strata admin are written as XXXH but some aren't. I have no idea what the significance of H is. Can anyone demystify things a little?