The end scene after Haven is written well, the various dialogues indicate various options. Someone is likely to be up to something with Arthur.
Could be Diana alone - she was alone with Arthur and there’s no way for Grey or 47 to tell who actually sent the message that it was going according to plan. Olivia likely dead here.
Could be Grey with Diana, similar explanation.
Similarly could be Olivia alone - she might have known about the various accounts all along and have sent a message that it’s all okay. Diana likely dead here.
Could be Grey with Olivia, similar explanation.
Could be Grey alone, he received a message that the money’s gone to Arthur along with surprise from Olivia and Diana.
Can’t be Olivia and Diana together or them with Grey as the interaction between Olivia and Diana then makes no sense.
Unlikely to be 47.