We’ve been seeing this issue also.
v1.4.0 is incompatible
v1.5.0 is compatible as noted in the commit at https://github.com/igniterealtime/openfire-restAPI-plugin/commit/649b8d97dfdaf2005ac955131622485fa8d4f4db
This issue is related to HazelCast PluginServlet RoomRemovedEvent ClassCastException.
We had hoped the PR at https://github.com/igniterealtime/Openfire/pull/1831 would resolve the issues we’re seeing with OF v4.6.3 and RestAPI-Plugin v1.5.0 but we’re still seeing problems. We’re still seeing this exception sometimes, but not with ‘GET chatrooms’ – with other endpoints instead.