Photo card always shows the same picture



Recently got Twitter’s approval to use photo card on, which is a custom domain used on a Tumblr blog.

The problem is that the picture displayed in the photo card is always the same one, no matter what post I tweet. Examples: (the photo does not matches the actual photo on the site) (actually I just realised it only shows on the previous tweet. This one and the next are not working)

This is the code I typed on my website:

<meta name="twitter:url" content="{Permalink}">
<meta name="twitter:site" content="@tumblr">
<meta name="twitter:creator" content="@davidesquimal">
<meta name="twitter:card" content="photo">
<meta name="twitter:image:src" content="{PhotoURL-500}">

Could anybody help me guess what is going on?