A waitlist of “notify me when it’s back” messages feels like one job: tell everyone the day stock arrives. In practice LINE, WhatsApp and Messenger each enforce a different rule on that exact message — one bills it against a monthly cap, one needs an opt-in and a template saved in advance, and one has no free way to send it at all.
Why one broadcast button doesn’t cover three platforms
On LINE, a restock update sent as a broadcast, push, multicast or narrowcast message counts the same way: once per recipient, against the account’s monthly message quota. LINE’s own pricing page lists all four send methods under “Sending methods that are counted as message count,” and only reply messages sent through a conversation’s reply token are exempt (LINE Developers: Messaging API pricing). The Free plan’s quota is 300 messages a month (LINE for Business: broadcast message) — more on what else burns through it. Message a 400-name waitlist at once on that plan and the extra 100 don’t fail quietly: the API errors out and those messages never go.
On Messenger and Instagram, a free-form reply only works “within the 24-hour window,” which Meta’s own Messenger Platform policy says “may contain promotional content” (Meta for Developers: Messenger Platform policy overview). Past that window, the standard tags cover only narrow, non-promotional cases — the Human Agent tag, the same mechanic that reopens a 7-day window on Instagram DMs, lets a person reply manually but not pitch a product. The only sanctioned way to send promotional content outside the window is Sponsored Messages, a paid ads product the same page names as the one exception that “can include both promotional and non-promotional content.” A free, compliant “it’s back!” ping to a waitlist gone quiet for days has no path here.
Capture the opt-in while you’re already answering them
That leaves WhatsApp, where Meta’s own developer documentation is direct: “before messaging people on WhatsApp, businesses are required to obtain opt-in permission” before sending a proactive message outside the 24-hour window (Meta for Developers: Get opt-in for WhatsApp). That opt-in must “clearly state that a person is opting in to receive communication from the business” and “clearly state the business’s name.”
As a recommended default — not a platform requirement — turn the moment a customer asks to be notified into that opt-in, rather than just a note to yourself:
Thanks! You’re on the list for [item name] — [shop name] will message you here on WhatsApp the moment it’s back in stock. Reply STOP any time to come off this list.
Save that line as a 1CS quick reply so every agent sends the same wording, and get the matching WhatsApp template approved on the account before the item actually restocks — sending it later is a business-initiated message once the 24-hour window has closed, and 1CS can only send a template Meta has already approved.
Set up in 1CS
Build an Automation rule so a “notify me” request gets tagged the moment it arrives, instead of sitting in a conversation someone has to remember to reopen. Automation runs as trigger → condition → action: trigger on a new message, condition it on the message containing words customers actually type — “แจ้งด้วยนะ,” “มีของแล้วบอกด้วย,” “restock,” “notify me” — and set the action to add a label such as “waiting: [item name].” This sits inside 1CS’s AI Agent tools; the Thai help center walks through the same trigger-condition-action screen in Automation rule (Thai only). When stock is back, filter the inbox by that label and work it top to bottom — the label only stops a request getting lost; the opt-in and template rules above still decide what you send.
What changes by channel when stock arrives
- LINE: every message to the list counts against the plan’s quota the same way, whichever send method triggered it. Size the waitlist against the free messages actually left that month, not against “everyone who asked.”
- WhatsApp: only message numbers whose opt-in reply is logged in the conversation, and only with an approved template.
- Messenger and Instagram: inside 24 hours of their last message, reply normally with the news. Outside it, the honest options are asking them to message first — which reopens the window — or paying for a Sponsored Message; there’s no free standing broadcast for a promotional update once the window has closed.
Keeping the waitlist isn’t the problem. The line a team sends today when a customer asks to be notified is what decides which of these three paths is still open tomorrow.
