Invalid content type with overlay

When testing in the Facebook debugger, I get the following error when the overlay is turned on:

Provided og:image URL, https://techdoods.com.au/wp-content/plugins/wonderm00ns-simple-facebook-open-graph-tags/fbimg.php?is_home=0&is_front_page=1&object_type=post&post_id=59&object_id=59&img=https%253A%252F%252Ftechdoods.com.au%252Fwp-content%252Fuploads%252FOpen-Graph-Default-Image.jpg could not be processed as an image because it has an invalid content type.

If overlay is turned off, the image works as expected, but missing the overlay of course.

The meta tag for the image looks like this:

<meta property="og:image" content="https://techdoods.com.au/wp-content/plugins/wonderm00ns-simple-facebook-open-graph-tags/fbimg.php?is_home=0&amp;is_front_page=1&amp;object_type=post&amp;post_id=59&amp;object_id=59&amp;img=https%253A%252F%252Ftechdoods.com.au%252Fwp-content%252Fuploads%252FOpen-Graph-Default-Image.jpg">

The og:image:url and og:image:secure_url tags are identical.

All images, including the overlay, are of appropriate sizes and types.

v3.3.0

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