Publishing erratum to arXiv and other best practices
Has the original paper been posted on the arXiv?

If so, I suggest updating it with a corrected version, and communicating clearly in the Comments field that this new version is a corrected one. (Also, I'd change the Journal-Ref to indicate that it doesn't exactly correspond to the publication.)

In terms of copyright, this may be in a grey zone in case you've signed away the rights to your preprint to the publisher. But if so, it is a grey zone academics have been comfortably treading for years.