If you don't have users' consent or permission to repost their content then you should not repost UGC. Taking permission is easier than it sounds, where you have different ways to do so. The most common way is to directly message the user and take explicit permission to repost their content.

Is it OK to repost on Instagram without permission?

Use the Repost for Instagram App

As long as you have prior permission to use someone's post, using this app (or another repost app) is compliant with terms of service. The Repost for Instagram app adds the creator's Instagram handle to the image you're resharing.

Why do people say do not repost?

so in conclusion, here are the dangers of reposting: the artists loses ownership of their art. no one knows who made it anymore, and don't care. the artists stop making art because all that happens is their art gets reposted without a source, and so they prefer to disappear off the internet entirely.