Why is this wrong: "ik reis naar amerika twee keer per maand." Am I missing a rule about word order?
Because the time adverb must be placed before the adverb of place.
For further information, please check:
Why would "keer" be singular here?
'Keer' and 'keren' can be used both here, but after a numeral, the singular is often used.
They didn't accept it, so I'll report it the next time I get it. Thanks as always!