Eos Boss fight

[DannyGoss60]

Ok the side missions leading up to the boss fight i have to talk with a new  group i forget the name in the game but they want to trad Gas for water then i get a Fail mission for not getting the Gas instead of water. Maybe i missed something it read after the Boss fight it read you take the what ever it was off the Head i didnt i hit the legs  first then the tender spot on the head still it read after the fight i failed still i  killed the Boss the Remnant Architect.

[AeromusPrime22]

After you initially down the architect you have to quickly run to head and get the remnant core.

Not sure about the failed mission for the gas/water trade though; that should be a prompt for you to choose after the fight.