To send an esignature image to Webmerge to get PDFed—it’s possible, but you need to do two things differently than for standard text fields as is demonstrated in the doc.
In the Webmerge template, you can’t just use an alias as you would with text fields. Instead, you need to add an image using their WSYWIG editor, then set the URL field for that image to the alias that you’re mapping the e-sig to in the HTTP Connector. In your HTTP connector mapping, you need to concatenate a header onto the e-signature image alias with a formula. Here’s the formula to use: @CONCATENATE("data:image/png;base64,",%%ESIG_SIGNATURE_IMG%%)