registry.registerMessageWillBePostedHook is undefined, when I trying to use it in web plugin. Other registers works pretty well but when i checked registry properties it is not visible. My mattermost version is latest (5.9.1). That register is defined in mattermost documentation so i think it should be available. Anyone used it?
Here i created the issue: https://github.com/mattermost/mattermost-plugin-sample/issues/37
i checked 5.10.0 mattermost version and it working here