I believe what you were offered was a change of cabin class by reservation change not a same-day cash upgrade that some airlines offer. I don't think JL does that while they offer cash upgrades from Y to PY.
I wouldn't talk to the manager in your situation since $280 for upgrade to J on a transpacific flight sounds too good to be true even from PY.
Last edited by kentauta; Sep 30, 2019 at 3:04 pm