In my experience, this is because the wall is desynced between users, so it may appear to be open on your end, but closed for other people. If it happens again, try closing the bar wall door thingy and pressing E around where the order thing is
Im having this issue too… my friend can use it but not me and im the host of the room. also i thought the bar was to be all inclusive as part of the deal. (as in its free to use)