Wedding is outdoors (or at least partially outdoors) on a farm, and the legal ceremony has already happened - this is the celebration of their marriage. They have sent out proper invites (if that matters). Not sure if it is too informal or not? I don't want to wear heels and I do not currently have any other flat shoes that go with my dress so would have to buy some tomorrow if the answer to my question is a resounding 'no'!
Thanks in advance