"Mně dal láhev mléka." - wrong word order, Correct answer: "Dal mně láhev mléka." or "Dal mi láhev mléka." - I am a native speaker.
Those are among the accepted translations. (Most of the course contributors are native speakers.)
"Mně dal láhev mléka." is a perfectly valid Czech sentence.
I'm a native speaker, too, and the hair on my neck is standing when I hear "Dal mně láhev mléka" - (or any other use of "mně" in the unstressed position, where "mi" belongs). But I am (painfully) aware that some speakers use it like that.
Proc ne "daval" ?
A proc ne "mě" ?
dával is repeated or describing the process of giving
mně is the right form for dative