To rez objects in your rental you need to be in the group and have the group tag activated. If you tried to rez and did not have the group tag activated the item is not in the region it is in your inventory. You may need to restart your Second Life viewer to find the object.
I am not responsible for lost items.
If you or someone you know needs a group invite follow the instructions for “Sending a group invite”.
I do not send group invites so it is up to the person who original procures the rental to send out group invites.
If you have a group invite and cannot rez try clearing the scene to the default and rezzing on the grass platform.