How to display JSON returned (from external REST API) in a Block? [my code attempt inside]
$block['content'] should be an array, like in the example for hook_block_view:

$block['content'] = array(
    '#theme' =&gt; 'feed_icon',
    '#url' =&gt; 'rss.xml',
    '#title' =&gt; t('Syndicate'),
  );


For more examples, see Examples for Developers project, block_example module.

If you are putting array there, it must be a renderable array. If it's not, then either:


Implode it into string. With nested arrays, it can get a bit complicated.
Put it as an element in $block['content'] array, and set $block['content']['#theme'] element to something that can theme it. More complicated, but also more versatile and cleaner solution.