Hello
i found several other topics about CSRF error but nothing quite helpful or relevant
when i embed in iframe a survey in wordpress, the first screen is ok but then after I press Submit i always got this error.
survey is minimal, 3 questions.
LimeSurvey version: Versione 5.3.26+220720
Own server or LimeSurvey hosting: own server, php 7.4, hetzner cloud
Survey theme/template: fruity vanilla

yes, i activated the IFrame embedding option
I also edited the Custom php.ini settings t othe following
max_input_vars =14000
session.gc_maxlifetime = 10800
max_input_time = 10800
max_execution_time = 10800
upload_max_filesize = 110M
post_max_size = 120M

==================
(Write here your question/remark)
 

thanks for your reply.
point by point

-Recheck the URL. Since a malformed URL is the most common cause of the 400 Bad Request error, make sure there are no typing or syntax errors in your URL.
the URL inside the iframe is correct, in fact the first screen loads perfectly. 400 error appears when click submit. is there any other URL I should check?

-Check your internet connection.
very fine

-Clear browser cookies.
done

- Clear DNS Cache.
done

- Compress the file.
which file?

- Deactivate browser extensions.
it happens on all browsers on many different pc's and mac even with no extensions.

Restart your system.
-done many times.

thanks again, waiting reply on thoose two items...