$ curl -I 'https://en.wikipedia.org/w/rest.php/v1/page/Wikipedia%3ASandbox/html'
HTTP/2 200 
date: Wed, 27 Dec 2023 01:48:15 GMT
server: mw1491.eqiad.wmnet
x-content-type-options: nosniff
cache-control: max-age=5
content-language: en
content-revision-id: 1191998422
access-control-allow-origin: *
vary: Accept-Encoding
last-modified: Wed, 27 Dec 2023 01:40:37 GMT
content-type: text/html; charset=utf-8; profile="https://www.mediawiki.org/wiki/Specs/HTML/2.8.0"
etag: W/"1191998422/efa972fc-a458-11ee-8729-c1319dbdd51a/view/html"
age: 0
x-cache: cp1106 miss, cp1106 miss
x-cache-status: miss
server-timing: cache;desc="miss", host;desc="cp1106"
strict-transport-security: max-age=106384710; includeSubDomains; preload
report-to: { "group": "wm_nel", "max_age": 604800, "endpoints": [{ "url": "https://intake-logging.wikimedia.org/v1/events?stream=w3c.reportingapi.network_error&schema_uri=/w3c/reportingapi/network_error/1.0.0" }] }
nel: { "report_to": "wm_nel", "max_age": 604800, "failure_fraction": 0.05, "success_fraction": 0.0}
set-cookie: WMF-Last-Access=27-Dec-2023;Path=/;HttpOnly;secure;Expires=Sun, 28 Jan 2024 00:00:00 GMT
set-cookie: WMF-Last-Access-Global=27-Dec-2023;Path=/;Domain=.wikipedia.org;HttpOnly;secure;Expires=Sun, 28 Jan 2024 00:00:00 GMT
x-client-ip: 74.71.26.214
set-cookie: GeoIP=US:NY:New_York:40.80:-73.98:v4; Path=/; secure; Domain=.wikipedia.org
set-cookie: NetworkProbeLimit=0.001;Path=/;Secure;Max-Age=3600
accept-ranges: bytes

$ curl -X POST -H "Content-Type: application/json" -H 'if-match: W/"1191998422/efa972fc-a458-11ee-8729-c1319dbdd51a/view/html"' --data '{ "html": "what" }' 'https://en.wikipedia.org/w/rest.php/v1/transform/html/to/wikitext/Wikipedia%3ASandbox'
{"message":"No stashed content found for 1191998422/efa972fc-a458-11ee-8729-c1319dbdd51a","httpCode":412,"httpReason":"Precondition Failed"}