Why does the error "Unable to verify your data submission." when uploading files in Yii2?

Question

Yii

I'm trying to upload a file. Uploads files fine if the file size does not exceed ~3MB, otherwise an error appears: Bad Request (#400) Unable to verify your data submission.
What is it connected with?

Answer 1

limit in php_ini ?

Answer 2

usually this error is due to a missing csrf. Try disabling validation.

Answer 3

As for disabling csrf - bad advice.
If everything was written correctly, then there should be no problems with it, and it’s better not to disable it, but to figure out how it works, this is a good protection against the destructive actions of hackers.
Other forums say to see if there are csrf headers in the main layout. Please send the contents of this tag; and also - how do you create a submit form.