Notes is a core feature of the OpenStreetMap.org website. It enables you to add a comment on the map to assist others in mapping/editing OpenStreetMap. Other users can respond to your notes, for example to ask for additional details if necessary.
Please do not use notes for general discussion 
Use this feature to report an error in the data or to give some additional information, for instance the name of a street or an address etc.
Don't post general comments. A note should relate to the map data at a specific location. If you want to contact the community about something more general, please use a more appropriate contact channel.
https://wiki.openstreetmap.org/wiki/Notes 

Tasking Manager
https://wiki.openstreetmap.org/wiki/Tasking_Manager

Japan 
https://wiki.openstreetmap.org/wiki/Japan#Communication_channels
https://wiki.openstreetmap.org/wiki/List_of_OSM_centric_Slack_workspaces#Slack_workspaces