Crawling and indexing are different controls
The original question asked how to keep an advertising landing page out of organic search without preventing its assessment for ads. That distinction still matters.
A robots.txt rule controls crawling for the user agents it applies to. It is not a reliable way to remove a URL from search results. A crawler must be able to retrieve a page to read a noindex directive on it.
Check the rules for the actual page
If the public page should remain accessible but not appear in organic search, inspect its response and indexing directives. Verify the robots.txt rules that apply to the relevant crawlers separately. Do not assume that one generic rule affects every Google crawler in the same way.
Use the advertising account’s diagnostics to check landing-page access. Noindex alone does not establish that the destination meets every advertising requirement.
Do not confuse this with privacy
Noindex is not authentication. If a page contains confidential material, protect access rather than merely asking search engines not to list it.
Test the deployed URL after a change, including redirects. Keep preview restrictions separate from the intended production behaviour.
See our website-upgrade checklist and Google Ads management.
This article has been updated to clarify the distinction between crawling, indexing and private access.