Twitter Card - Image not showing

Question

I have this code:

<meta name="twitter:card" content="summary" />
<meta name="twitter:site" content="@myTwitterUser" />
<meta name="twitter:creator" content="@myTwitterUser" />
<meta name="twitter:title" content="My title" />
<meta name="twitter:description" content="This is my description" />
<meta name="twitter:image" content="http://www.this_is_my_domain.com/img/logo-a-366x366.png">

The image exists, its type is PNG and its size is 366x366. Then I check it in https://cards-dev.twitter.com/validator this tells me

*.this_is_my_domain.com/ is whitelisted for summary card

INFO: Page fetched successfully
INFO: 23 metatags were found
INFO: twitter:card = summary tag found
NFO: Card loaded successfully

But no image is shown. I waited like 2 days to prevent catching.

Any ideas?

EDIT:
I had .jpg picture on the server bu the call was .png :/

Answer 1

http://sproutsocial.com/insights/social-media-image-sizes-guide/#twitter claims that the minimum image size (in pixels) that will show up in a Twitter stream is 440 x 220 (2:1 Ratio).

https://blog.hubspot.com/marketing/ultimate-guide-social-media-image-dimensions-infographic claims it should be at least 506 x 253.

Either way, your image size of 366 x 366 doesn't meet the minimum width requirement. It makes sense to make your image for social media sharing significantly larger. If you want to share on Facebook, they require at least 1200 x 600.