The funny thing is that simply changing the text color to black causes the green-on-black to pass all those metrics, with the blue-on-black passing everything but WCAG AAA with the normal font (but still passes on the larger font).
(Same result using #64C567 for the green bubbles, which a sibling pointed out is the correct value.)
The colours do not pass the A11Y standards, which means people with poor eyesight can't read the messages properly.
This did made me curious to see if the blue background passes - and it doesn't either. https://color.a11y.com/ContrastPair/?bgcolor=047aff&fgcolor=...
At least the blue background passes WCAG AA with larger sized text, while the green doesn't pass at all.