This issue persists...
I have a bot with 500 followers and sending nearly 10,000 responses per month ... but send 1 message to a group of 250 and it's "game over" ... terrible design.
As a follow-up... this document clearly says there is a 1.000 message limit for "Free" LINE Official Accounts, yet the limit appears to be a reach of 500, not 1.000 messages. A single message sent to a group is counted by each member that reads the message. This is a 'reach' limit, not a message limit. Further, broadcast messages are counted by each delivery point, again this is 'reach' not a message count limit (which seems to defeat the purpose of using the tool).
How are others dealing with this issue? https://help2.line.me/official_account_jp/web/categoryId/20006345/pc?lang=en (See section Sending Message | Sending additional messages beyond the free message limit )