What is wrong with "I will tell you everything"
Nothing. Report it if they don't accept it.
It was accepted in my case :)
"I will say everything to you." I know it's not natural, but it should be accepted.
I will say everything to you = Ich werde alles zu dir sagen
Which means that you will just say everything that exists...
That's not possible
I would have used the word "erzählen" instead of "sagen". Am I wrong or are both acceptable?
Most of the times it's correct. Here, 4 this example, u can also use 'erzählen'.^^
Nothing's wrong with it. I think they just forgot to add it...
I will say you everything? Marked as wrong.
that's what Ned said