Dutch 1 - 'Mogen we ... alstublieft'

I keep being told ‘mogen we … alstublieft’ is incorrect then being shown ‘mogen we … alstublieft’ as the correct answer. It’s not a spelling or grammatical error, so what’s going on here? It must be really confusing to new learners, it’s just really annoying to me as a more experienced learner. Thank you.