Change ‘One or more fields have an error. Please check and try again.’

See Editing messages

I would like to change that message dynamically- with PHP, if there are any hooks for that.

You can use the wpcf7_display_message filter hook.

I use it like this: apply_filters( 'wpcf7_display_message', 'My custom message' ); but the message does not change. Any ideas?

It’s ok, I found an example here: https://stackoverflow.com/a/65037715/2257230 and it works just fine now.

Thank you for your help!!!