Get full url of asset, not just the path
You can slice the / from the end of {{ siteUrl }} and combine it with getUrl relative path:

&lt;meta property="og:image" content="{{ siteUrl|slice(0,-1) }}{{ entry.fieldName.one().getUrl('kafel620') }}"&gt;


This will produce expected path:

&lt;meta property="og:image" content="http://site.local/assets/images/ramPamPam/headers/_kafel620/tagiatelle.jpg"&gt;