Києв or Kиїв -- what is the accepted spelling this week?
it is the change of the word stem: Kиїв (Kyiv, nominative) but y Києвi - in Kyiv, locative.
In other cases too: Києва, Києву, Києвом, Києве (like in Kyiv's anthem - "Києве мій")
In nominative case it is Київ, in all others the letter ї is changed into є due to phonetic rules. Not to be confused with the Russian name for Kyiv which is "Kiev".
Odd wording here, should be: we are advertising.../we can advertise...; we advertised...; we will advertise. Could be: we advertise new restaurants in Kyiv