Button with dynamic URL

On one of my websites with GPP Pro I have a CPT with custom taxonomies and custom fields (default WP custom fields, not ACF or Metabox). I want to fill some blocks with dynamic data on this page. Everything about the dynamic data works fine, except the URL in the button.
The label of the button is always the same, so I created (and filled) a custom field called affiliate_url for the URL. But whatever I do, the button won’t make it to a decent hyperlink. What did I miss???