Twitter cards doesn't work

Hi,

I found this topic: https://www.ads-software.com/support/topic/how-to-update-twitter-cards-meta?replies=5

So, I put this code in my theme function.php:

function tweakjp_custom_twitter_site( $og_tags ) {
	$og_tags['twitter:site'] = '@techsou';
	return $og_tags;
}
add_filter( 'jetpack_open_graph_tags', 'tweakjp_custom_twitter_site', 11 );

But now I have this error message:

https://www.dropbox.com/s/fzxgj2f73jcfts4/Screenshot%202014-01-09%2018.59.22.png

Please, can you help me?
Thanks

Try adding the following Jetpack add-on instead to customize the Twitter Card value. You can upload the plugin by going to Plugins > Add New > Upload:
https://i.wpne.ws/TI3x

Once you’ve done so, could you go to this page and apply:
https://dev.twitter.com/docs/cards/validation/validator

Let me know if it helps.

Many thanks, Jeremy.
I uploaded the plugin and modified the TW username in the plugin jp-cus-tw-site.php, but it doesn’t work. There’s no summary card in twitter timeline when JetPack publicize a new post.
I try JetPack Debug, everything looks ok.

After a while a Twitter card was activated very well.
But have I to validate every post with Card Validator?

You only have to validate your site once, and once it’s approved by Twitter things should work properly for each one of your posts.

Thank you very much, Jeremy.
I had already validated my site before installing your plugin.

It seems to work fine, but a curious thing happens: immediately after its publication, the post goes regularly. It appears on Twitter with its summary card. But that summary card disappears after a few minutes from the Timeline. And it does not reappear again.

That seems like an issue with Twitter. You might want to post in the Twitter Dev forums to see if someone else ran into similar issues in the past:
https://dev.twitter.com/discussions

Sure, I post in Twitter Dev forums.
Thank you very much for your help!