Pay Phone Coin Box Removals

[eastmandg]

I just acquired a vintage 70's AT&T SWBell pay phone.  Have key & t-bar.
When attempting to remove orange coin box... it won't dislodge more than an inch out of the vault.  It won't go back in either.  How can I get this thing out??? 

[HarrySmith]

There is a locking tab on the top. I am not sure how it works but I am sure someone here does and will chime in.