Coaching client check-ins over iMessage: photos, tapbacks and voice notes

Who uses iMessage for coaching check-ins?

iMessage check-ins suit online personal trainers, nutrition and habit coaches, and the coaching apps they run on. ZeroSettle is an iMessage API: a real phone number on real iMessage, running on Apple hardware we operate for you, that your code texts customers from and hears back on through a bearer token and signed webhooks.

The problem is scatter: check-in forms get skipped, in-app chat needs the app open, and client messages split across Instagram, WhatsApp and SMS. Studios chasing intro-class visitors have a different job (fitness studio follow-up), as do tutors writing to parents (tutoring parent updates).

How iMessage coaching check-ins work, step by step

The client starts the thread once, your scheduler sends a prompt every day, and ZeroSettle’s webhook turns each reply into a row your app logs. ZeroSettle does not schedule sends; your job decides when.

1. Kickoff. The welcome email carries a prefilled sms: link (“Hi Coach Dee, it’s Sam”). Once the client has texted, links in later messages are tappable. See getting clients to text first.
2. Daily prompt. At the client’s chosen time, your job calls POST /api/imessage/send and stores the message id it returns.
3. Tapback answer. The client double-taps the prompt (or touches and holds it) and picks thumbs-up or thumbs-down. Your webhook gets reaction.received with reaction set to like or dislike and target_id pointing at the prompt, so the day is logged as hit or missed, as in tapback surveys.
4. Photos. A meal or progress photo arrives as message.received with kind: "image". Your server fetches it with the same bearer token for the client’s file or your own vision model.
5. The coach answers with a voice note sent as audio_b64, a tapback through POST /api/imessage/reactions, or a text from the ZeroSettle console.
6. Routine versus hard moments. Your own model can answer routine replies and flag the hard ones (a missed week, an injury) to the coach. ZeroSettle’s terms require disclosing AI replies unless that is evident from context, and rule out automating critical health advice without a qualified professional supervising, so injury and health questions belong with the coach.

Example conversation: a day-12 check-in

In this day-12 check-in the client misses the target with a thumbs-down, sends a dinner photo and gets a voice note back from the coach’s number.

Setup: a daily prompt job plus tapback logging

One script covers the loop: a daily send that stores the prompt’s id, a voice-note sender, and a receiver that verifies ZeroSettle’s signature (copied from the docs’ webhook steps), logs tapbacks and files photos.

# checkins.py: run with  uvicorn checkins:app --port 8100
import base64, hashlib, hmac, json, os, pathlib, time
import requests
from fastapi import BackgroundTasks, FastAPI, Request, Response

BASE = "https://portal.zerosettle.io"
AUTH = {"Authorization": f"Bearer {os.environ['ZEROSETTLE_TOKEN']}"}
SECRET = os.environ["ZEROSETTLE_WEBHOOK_SECRET"]
app = FastAPI()
seen: set[tuple[int, str]] = set()           # use your database in production

# Your app's storage and coach inbox: replace these stubs.
def save_checkin(client, message_id): ...
def checkin_for_message(message_id): ...     # the check-in whose prompt has this id, or None
def retry_later(client, after_s): ...
def flag_for_coach(client, code): ...
def notify_coach(m): ...
def add_to_client_file(handle, photo): ...
def route_reply(m): ...

def verify(header, raw):
    try:
        parts = dict(p.split("=", 1) for p in header.split(","))
        t, v1 = int(parts["t"]), parts["v1"]
    except Exception:
        return False
    if abs(time.time() - t) > 300:
        return False
    expected = hmac.new(SECRET.encode(), f"{t}.".encode() + raw, hashlib.sha256).hexdigest()
    return hmac.compare_digest(expected, v1)

def send_prompt(client):                     # your scheduler: daily, one client at a time
    text = f"Day {client.day} check-in: did you hit {client.protein_g}g protein today? 👍 or 👎"
    r = requests.post(f"{BASE}/api/imessage/send", headers=AUTH,
                      json={"to": client.handle, "text": text}, timeout=90)
    if r.ok:
        save_checkin(client, message_id=r.json()["id"])    # the id a tapback points at
    elif r.status_code in (429, 503):                      # line busy or briefly unreachable
        retry_later(client, after_s=int(r.headers.get("Retry-After", 60)))
    else:
        flag_for_coach(client, r.json()["error"]["code"])  # recipient_opted_out, awaiting_reply

def send_voice_note(handle, path):           # recorded by the coach in your app
    audio = base64.b64encode(pathlib.Path(path).read_bytes()).decode()
    requests.post(f"{BASE}/api/imessage/send", headers=AUTH, timeout=120,
                  json={"to": handle, "audio_b64": audio, "audio_format": "m4a"})

def handle(event, m):
    if event == "reaction.received":
        checkin = checkin_for_message(m["target_id"])
        if checkin and m.get("reaction") in ("like", "dislike"):
            checkin.log(hit=m["reaction"] == "like")       # keep the latest per check-in
        else:
            notify_coach(m)
    elif m.get("kind") == "image" and m.get("image"):
        photo = requests.get(BASE + m["image"]["url"], headers=AUTH, timeout=30).content
        add_to_client_file(m["handle"], photo)
    else:
        route_reply(m)                       # routine: your model; hard moments: the coach

@app.post("/webhook")
async def webhook(req: Request, tasks: BackgroundTasks):
    raw = await req.body()
    if not verify(req.headers.get("X-ZeroSettle-Signature", ""), raw):
        return Response(status_code=401)
    ev = json.loads(raw); m = ev.get("message")
    if m is None or ev["event"] not in ("message.received", "reaction.received"):
        return Response(status_code=200)     # your own sends echo back; typing has no message
    if (m["id"], ev["event"]) in seen:
        return Response(status_code=200)     # retries carry the same id and event
    seen.add((m["id"], ev["event"]))
    tasks.add_task(handle, ev["event"], m)
    return Response(status_code=200)

Register the receiver with PUT /api/imessage/webhook and store the signing secret; it is shown once. Answer with a 2xx within 10 seconds and do the work afterwards, as the background task does. On a timeout or any other status, ZeroSettle retries three more times, after 1, 5 and 20 seconds.

Details that matter for coaching

• Emoji tapbacks. On recent iOS a client can react with any emoji, Memoji or sticker, but ZeroSettle’s docs name six reaction types (love, like, dislike, laugh, emphasize, question). Score only like and dislike; send anything else to the coach.
• One photo per text. A message with three meal photos delivers only the first, so ask clients to send each meal on its own.
• Voice notes expire for the client. By default Messages deletes an audio message 2 minutes after it is played unless the listener taps Keep. ZeroSettle keeps your copy at GET /api/imessage/messages/{id}/audio; formats and sizes are in what an iMessage API can send.

Limits and consent for coaching check-ins

After the kickoff text, every check-in is an ongoing conversation that ZeroSettle’s new-contact limit never touches, and tapbacks never count. The rule that matters is the cap on unanswered messages.

Source: ZeroSettle iMessage API docs, “Errors, limits, and compliance”. Message volume is unlimited on both plans.

The limit math for one coach’s roster

• 80 clients on Pro, onboarded with the kickoff link: no limit applies. Sends go out one at a time per number, normally 2–5 seconds each, so if all 80 prompts share a 7:30 PM slot, the last goes out about 3 to 7 minutes later.
• Moving 80 existing clients by texting them first: 16 days at Pro’s 5 a day, and on iOS 26 a cold first text can be filed under unknown senders with no notification. Asking them to text first uses none of the limit and avoids that.
• A quiet client: if days 12 and 13 go unanswered, the day-14 prompt returns 403 awaiting_reply and nothing is sent. Any reply resets it, a 👍 included. This applies on every plan, and repeated messages to people who never answer get numbers flagged, so pause prompts after two quiet days.

When ZeroSettle is not a fit for coaching check-ins

ZeroSettle is the wrong tool for check-ins in these cases:

• You are a licensed dietitian or clinician who may be covered by HIPAA and check-ins carry patient health information. ZeroSettle’s terms prohibit that without a signed Business Associate Agreement, the written agreement HIPAA generally requires before a vendor handles that information for you. Whether HIPAA applies to you is a question for counsel; this isn’t legal advice.
• You run group coaching chats. Conversations are one to one; group chats are on the roadmap.
• Most clients use Android. There is no SMS fallback, and the kickoff sms: link opens the SMS app on Android.
• You coach from video form checks. Video isn’t supported in either direction.
• You need proof a client played a voice note. The API reports that a message left the line, not that it was read.

How much does iMessage for coaching check-ins cost?

Check-ins cost the plan price: ZeroSettle charges no per-message fees, and message volume is unlimited on both plans.

Both plans are billed monthly with a 30-day money-back guarantee on the subscription, and your own model on the webhook uses no ZeroSettle AI credits. Compare ZeroSettle plans, browse more iMessage use cases, or get a number.