As of today versions of the Castro app prior to 2025.4.1 (released April 2025) will not work with Castro's servers. All users of older app versions are encouraged to update. We've taken pains to continue to avoid these kinds of forced updates, but in this case it's unavoidable.

Since Castro migrated to account profiles at the end of 2024, this allows us to align on a single account structure and will simplify the backend code along with improving security.

Please email support with any questions.