I suspect that it may be a set dialplan issue. Did you ever create one, and download to the set? Check the 3CX Activity Log to see if an Invite is even reaching 3CX.
As I recall, when setting up that type set a few years ago. There is no initial dialplan, so digits are not sent until a timeout, or end of dialling "key" (can't recall what the end of dialling key was used). I don't recall digits being blocked at all.