HasanMerkit based on the error message, it might be caused by the Flarum Subscriptions extension being disabled.
Subscription is an optional dependency of FoF Follow Tags.
Follow Tags is a required dependency of Follow Users.
There must be a check somewhere missing to make the extension work without Subscriptions, or maybe a requirement for Subscription was intended but is missing.
Since there is no requirement defined in the extension meta, it's possible the order the extensions are enabled in affect the error. It might only happen if this extension and Subscriptions were enabled in one specific order.
