WorldCat Discovery only accepts images using the SSL protocol so you must provide a link that uses https:// and not http://.
Also note that the logo image cannot exceed 80 pixels in height and 275 pixels in width.
Additional Information
Logo images need to be in one of the following image formats
If wanting to use a .svg format for the logo, you need to designate the width and height in the <svg> tag of the file. If this is not done it will appear when you use the Test URL but will not display as the logo on the Discovery page without this information in the HTML coding.
Example: https://upload.wikimedia.org/wikipedia/commons/archive/1/1b/20140514074814%21OCLC_logo.svg
For more information on updating your logo, please visit the Logo Settings help page.