Cliffhaven Kitesail

• WOTC Official Reminder Textofficial rules
  Equip — Equip [cost] ([cost]: Attach to target creature you control. Equip only as a sorcery.)

• WWizards of the Coast2020-09-25
  Official Ruling
  Attaching an Equipment with its enters-the-battlefield triggered ability isn't the same as using its equip ability. You don't pay mana for the attachment, and if the Equipment enters at a time you couldn't cast a sorcery, you can still attach it to a creature you control.
• WWizards of the Coast2020-09-25
  Official Ruling
  If the target creature becomes an illegal target, the Equipment remains on the battlefield unattached.

Rulings via Scryfall