🚨 Error: Failed to execute 'sendBeacon' on 'Navigator': Beacons are only supported over HTTP(S).

Details
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**Error report:** [link](http://go/ampe/CJ6v2LLM-YSBhAE)
**First seen:** Mar 11, 2021
**Frequency:** ~ 164/day

Stacktrace
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Error: Failed to execute 'sendBeacon' on 'Navigator': Beacons are only supported over HTTP(S).

    at WindowInterface (extensions/amp-analytics/0.1/transport.js:269:23)

    at sendRequestUsingBeacon (extensions/amp-analytics/0.1/transport.js:118:16)

    at sendRequest (extensions/amp-analytics/0.1/requests.js:282:24)

Notes
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`@lannka` modified `extensions/amp-analytics/0.1/transport.js:269-270` in [#19102](https://github.com/ampproject/amphtml/pull/19102) (Nov 3, 2018)
`@rsimha` modified `extensions/amp-analytics/0.1/transport.js:116-119` in [#21212](https://github.com/ampproject/amphtml/pull/21212) (May 16, 2019)
`@jonathantyng-amp` modified `extensions/amp-analytics/0.1/requests.js:278-287` in [#22454](https://github.com/ampproject/amphtml/pull/22454) (Jun 21, 2019)

**Seen in:**
- 03-12 Nightly (2145)

**Possible assignees:** `@jonathantyng-amp`, `@lannka`

/cc @ampproject/release-on-duty

Start by inspecting extensions/amp-analytics/0.1/transport.js around lines 116-119 and 269-270, then trace the request flow in extensions/amp-analytics/0.1/requests.js around lines 278-287. The issue provides the failing browser error and stack trace, but does not define the expected behavior or a named test, so confirm the intended handling for non-HTTP(S) contexts before determining what done means.

Written by the indexing model from the issue text.