My billow did the same for me at first MotoMudder, no connection.. good old non spring loaded center pin ecigs heh, the subtank that came with mine has squashed the 510 pin pretty low over the months. Thankfully the billow v2 has an adjustable center pin copper screw thingy. I had to use a screwdriver to loosen it to start with but after that can just adjust the height with a thumb or finger... actually a bit too loose for my liking but I guess it saves making my subbox any more recessed since it will screw itself back in if you go too far
I think by default the billow v2 may have a really low pin anyway.. seems low to me at least.
Some people in the past have recommend pulling the center pin up on the ecig/mod itself a bit after they have been squashed over time, but the few ecigs / mods I have tried that on it has only ever been a temporary fix at best, at worse has ruined them
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Edit: oh, my billow is still stable at 0.4 ohms and the screw hasn't moved in the slightest for some hours now.. phew !, think she's good
.. I guess it was probably user error, like maybe because of the tinyness of the screws I was over timid in applying pressure that first time. It is a teeny little fiddly deck to work on lol, even coming from the subtank rba decks.. reminds me more of rebuilding protank etc coils