Why Is Wearable Data Missing or Delayed?

Your webhook is quiet, or a workout the user just finished isn't in your API yet — and nothing is technically broken. The single most common cause: the data hasn't finished syncing yet. A reading has to travel device to phone app to the provider's cloud before any webhook can fire, and each hop runs on its own schedule. Wearable pipelines are near-real-time, not instant — set that expectation first, then work down the causes below.

Set expectations: the sync chain

New data does not appear the instant a rep, a heartbeat, or a run happens. It moves through four stages, and a webhook to you fires only at the very end:

device (watch/ring)  →  phone app (vendor)  →  provider cloud  →  webhook  →  you

• Device to phone: the watch or ring syncs over Bluetooth on its own schedule — often every few minutes to hourly, and sometimes only when the vendor app is opened.
• Phone to cloud: the vendor app uploads to the provider's cloud, again on its own cadence.
• Cloud to you: only once the provider's cloud has the data does it push a webhook (or make it available to poll).

So a gap of minutes — occasionally longer — between "the user did the thing" and "it's in my API" is normal, not a bug. Rule that out before deep debugging. For the bigger picture of how these pipelines work, see the wearable data APIs overview.

Most likely causes (ranked)

1. The data hasn't synced device → phone → cloud yet. The wearable syncs on its own schedule, and webhooks fire only after the provider's cloud has the data. This is the number-one cause of "missing" data.
2. You expected history but only get data from connection-time forward. A new connection yields data only from that point onward unless you make an explicit historical/backfill request — and some providers only expose recent data.
3. A webhook delivery failed and was retried or dropped. If your endpoint returned a non-2xx status or timed out, the event never landed. Make your handler idempotent and return 200 fast.
4. For an aggregator like Terra: the user connected but hasn't synced, or you never requested history. "Connected" is not "has data" — the user still has to open the vendor app and sync, and prior history still needs a backfill call.

How to fix it

Step 1: Force a sync and confirm in the vendor's own dashboard

Have the user open the vendor app (Garmin Connect, Fitbit, Oura, etc.) and force a sync — usually "pull down to refresh." Then confirm the reading actually appears in the vendor's own web dashboard or app before blaming the API layer. If it isn't even in Garmin Connect, no API can have it yet.

Terra states this plainly: "If the wearable hasn't synced to the respective app on the end user's phone, or if the app has not synced to the cloud, Terra will be unable to retrieve that data." The same logic applies to every provider.

Step 2: Wait out normal latency before deep debugging

If the data is in the vendor dashboard but not yet in your API, give the pipeline a few minutes. Near-real-time means the cloud-to-you push has its own small delay. Rule this out first — a surprising share of "missing data" reports are just impatience with a normal source-side lag.

Step 3: Request historical data explicitly (don't assume backfill)

By default a new connection only yields data from the connection point forward. To build a historical profile you must make an explicit backfill request, and how far back you can go is provider-dependent. With Terra, request a date range on the REST endpoint:

curl --request GET \
  --url 'https://api.tryterra.co/v2/activity?user_id=USER_ID&start_date=2026-05-01&end_date=2026-06-30&to_webhook=true' \
  --header 'dev-id: YOUR_DEV_ID' \
  --header 'x-api-key: YOUR_API_KEY'

Note Terra's 28-day async rule: for ranges longer than 28 days it sends the data asynchronously over your webhook even if to_webhook is false, because a large payload would otherwise hang the request. Match the terra-reference header on your request to the terra-signature on the eventual webhook to know the transfer completed. Verify the exact endpoint and params against the current Terra docs. See the Terra integration guide for the full setup.

Step 4: Make sure your webhook actually accepted the delivery

If your endpoint returns a non-2xx status or times out, the provider counts it as a delivery failure — some retry with backoff, some drop the event. In Terra these show up as 400 or 500 errors in Dashboard, then Payload History. The fix is structural:

• Return 200 (or any 2xx) immediately, then process asynchronously. A slow or erroring handler looks exactly like "webhooks aren't firing."
• Make the handler idempotent so retried deliveries don't double-insert.
• Check that no auth middleware, WAF, or redirect (301/302) sits in front of the webhook path.

This is the same failure pattern behind Strava webhooks — see Strava webhook not firing for the handshake-and-handler details.

Step 5: For aggregators, isolate the connection from the delivery path

If a user is "connected" through an aggregator but you see no data, walk this Terra checklist to find where the break is:

• Not synced yet — force a sync; confirm data in the vendor's own dashboard (Step 1).
• Wrong account — the user may have authenticated a different or empty vendor account.
• Destination misconfigured — missing dedicated credentials surface as 400/500 in Payload History.
• Force a backfill to isolate the fault — in Terra, go to Dashboard, then Tools, then Debug, then Users, and request a backfill for that user_id. If data does come through this way, the connection is fine and your realtime webhook path is the problem. (Verify the menu path; this requires a recent Terra SDK.)

Still stuck? Quick triage

• Is the reading in the vendor's own app/dashboard? If not, it's a sync issue, not an API issue.
• Is the data after the user's connection date? Data before it needs an explicit backfill request.
• Does your webhook return 2xx within a couple of seconds, before doing any heavy work?
• Is your handler idempotent so retries are safe?
• Have you checked the provider's payload/delivery history for 4xx/5xx on your endpoint?
• Have you simply waited a few minutes to rule out normal near-real-time latency?

If data flows on a manual backfill but never arrives in realtime, the connection is healthy and the problem is on the delivery path — focus there. For choosing between aggregators and direct integrations, see the wearable data APIs guide.