What’s the layout of the modules? Are they 2s2p, or 4s1p? If 2s2p, then you either need the last pack to have the nickel strip connecting all 4 cells, or you need to bridge it with a wire like this:
You would use a full length nickel-plated copper tab in that last module, like I drew in the picture with the grey lines. Maybe one of your modules already has a full sized one, maybe you have a spare one / need to order one. If you don’t have it (all your tabs are only 2 cells long) then you can resort to using a wire.
Oh shoot, I just realized how your last setup worked; you have 5 full-length copper tabs actually. That means you’ll need to cut 4 of them in half. (make sure the sides can’t touch, so like, cut a small slit out of the middle)
Yes, you could use wires instead of the bus bars, but I would suggest just ordering some; they’re cheap after all.
If you want the standard connection, you will need 8 series bus bars and you will need to rearrange the tabs. You will need extra 2P tabs as 2S2P modules have 1 4P tab and you can use it for one side so you need 4 2P tabs. Contact me and we could arrange some for the price of shipping.