Returns follow the policy of the retail partner that fulfilled your order, since they hold the stock and process the refunds. The notes below describe what their policies usually look like.
The most common eyewear return is a diopter that turned out half a step off. Partners treat it as an ordinary return: send the pack back, order the next strength. Testing your reading distance with a phone before ordering, as the strength guide shows, prevents most of these round trips.
A cracked lens, a missing pair from a multipack or a bent hinge out of the box are on the partner to fix, usually with a replacement at no cost. Photograph the issue and open a claim from your order history; it is the fastest route.