"Do you have a razor?"
Translation:Você tem um barbeador?
I found "barbeador" in my vocab list and used "practice word" a few times until this question came up. You are right, it rejected "uma navalha de barba" but was happy with plain "uma navalha". I've asked for your sentence to be accepted. Interestingly, another question asks for a translation of "I need a razor" and it accepts "Eu preciso de uma navalha de barba".
It's probably because "tem" is the conjugation of "ter" for "you", but also for "he" and "she". So "Tem um barbeador?" could also mean "Does s/he have a razor?". But "Você tem um barbeador?" is unequivocally "Do you have a razor?". (Although "Do you have a razor?" can both be "Você tem um barbeador" or "Vocês têm um barbeador?")
Because 3rd Person covers so much in BT PT and even in EU PT, it just is not a good idea to leave off the pronouns until context is established.
This is more of an issue on Duolingo too because the Owl does not recognize most punctuation (including all those that end sentences).
But also because with most verbs the 3rd Person Singular Simple Present is also the 2nd Person Singular Imperative so can read as, "Have a razor!"
In this sentence in particular though, in Brazil without a pronoun then "tem" also means: "There is a razor."
One more way to say, "Do you have a razor?" is "[Tu] tens um barbeador?" and not only is it okay to drop the pronoun with this construction as it only applies to 2nd Person Singular, but it cannot be confused for any other tense or mood. However, this type is only used in some places in Brazil, but more likely in all the other PT places outside (Europe/Asia/Africa), especially if one is familiar enough to ask someone else for a razor.