Safe assembly of antique Italian four poster bed frame
3rd pic down, that gap proves it is not assembled correctly. Clamp it to get rid of the gap and then tighten the bolt.
A spanish windlass would work for this. A long rope goes round the bed frame 4 times then a bar is used to twist the 4 strands and tighten.
Protect the wood as the rope can cause a huge load and damage it.