This scope lets an app "Post messages in approved channels & conversations"
For new Slack apps,
chat:write replaces both
chat:write:bot. Here's a bit more detail on why perspectival scopes are disappearing.
This OAuth permission scope works with these Web API methods.
chat.delete- Deletes a message.
chat.deleteScheduledMessage- Deletes a pending scheduled message from the queue.
chat.postEphemeral- Sends an ephemeral message to a user in a channel.
chat.postMessage- Sends a message to a channel.
chat.scheduleMessage- Schedules a message to be sent to a channel.
chat.update- Updates a message.