Error in getEmbeddedSigningUrl

Can’t get past this in my APEX code: Method does not exist or incorrect signature: void getEmbeddedSigningUrl(Id, System.Url) from the type dfsle.SigningService.

More context:

 String returnRedirect = 'https://<someURL>/s/paperwork-complete';

 Url signingUrl = dfsle.SigningService.getEmbeddedSigningUrl(myEnvelope.id, new Url(returnRedirect));

 return signingUrl.toExternalForm();