Send a template chat message

Send one message to the chat of a saved template. The first message of a template without a chat starts its chat. A message can name a brand_kit_id, which becomes the chat kit. A message without brand_kit_id keeps the chat kit. A message with brand_kit_id null has no kit, and the chat has no kit from then on. A chat without a kit builds without a brand. A words message that asks for no change, such as a greeting alone, succeeds with outcome needs_detail and a short reply: it keeps the chat draft and costs 0 credits. A chat has one pending message at a time. It keeps its newest 100 messages; older settled messages drop off. A words or HTML message costs 25 credits. A source image costs 50 credits. The first message of a new blank template costs 50 credits. A source message makes no model call and costs 0 credits. A failed message keeps the previous draft and releases its reservation. All available credits, including free monthly credits, can pay for AI work. An account without enough available credits answers 402 insufficient_credits and holds nothing. Read message.progress for elapsed time, the current stages, and recent successful timing estimates. Estimates use the last 48 hours for the same model route and task when enough samples exist; completion time varies.