Synapse
curl --request DELETE --header "Authorization: Bearer <auth token from element admin>" "https://homeserver.url/_synapse/admin/v2/rooms/<url encoded room ID>" -d '{"purge":true}'
curl --request DELETE --header "Authorization: Bearer <auth token from element admin>" "https://homeserver.url/_synapse/admin/v2/rooms/<url encoded room ID>" -d '{"purge":true}'