Anyone who has put together a ready to assemble piece of furniture, has experienced this issue. When assembling our solid wood furniture, make sure that the cam-lock pin is screwed into the wood only until the end of the thread and no further. If the pin is screwed in too far into the wood, it will be too short and the cam-lock will not be able to grab it to tighten the assembly.
If you have screwed the pin in too far, unscrew the pin so that it is screwed only until the end of the thread - and try to assemble the unit again. Your cam-lock should be able to lock and tighten at that time.