I believe there is an issue in Web Fonts.
Create any email template, then add an email using a remote web font url.
I’m using the URL https://fonts.googleapis.com/css?family=Poppins but any font url will probably do the same thing.
The process is described → Fonts
Then, switch the email from design to preview mode. You will see in the designer an error appear.
java.io.IOException: Server returned HTTP response code 400 for URL: https://fonts.googleapis.com/css
When this template is sent to Workflow, the error message is slightly different.
2025-05-21 15:48:48.054 +10:00 [Warning] Error (C:\Users\planetpress\Connect\logs\Mergeengine\Mergeengine-2025-05-21-(10580).log:2588) [2025-05-21 15:35:35,850] ERROR [main] com.objectiflune.contentcreation.html.mergeengine.impl.HtmlMergeToPDF.cloneHTMLForWebOutput(d.java) java.io.IOException: Server returned HTTP response code: 400 for URL: https://fonts.googleapis.com/css2