After the English defeated the French at Agincourt, Henry V found himself with quite the number of prisoners and came to the conclusion that he had too many and so he decided that killing off a few would make them easier to handle, feed, control etc.
I've heard accounts that some of the Engish soldiers either protested a bit or were hesitant to go through with the killings.
Was this purely due to a moral code? I would've thought that killing an unarmed prisoner, who had surrendered, would not be a good look and be seriously frowned upon by other nations and peoples?
Was it more to do with the fact that a French Knight represented quite a bit of money. Holding a French nobleman for ransom and getting their family to pay for their release could bring in quite a bit of money and so it would be understandable for someone to be a bit hesitant to just kill one and throw the money out of the window, as it were.
Or was it a bit of both?
I must point out that it wasn't after the battle, it was during, and there were circumstances at play that turned the decision for Henry at the time. On why some of the English were hesitant about it, your second point is much closer to the mark, as the following previous answers will explore. More can always be said from anyone with the knowledge, so if anyone else would like to contribute further, don't let this post stop you!
For the meantime, here are some previous answers that explore the specific matter of the French prisoners at Agincourt. u/MI13 has four relevant posts:
For bonus, u/The_Truthkeeper looks at Ghillebert de Lannoy, one of the captives who managed to survive the executions.