In case the default poll invitation sent by SignSpace system is not successful for any technical reasons, the creator of the poll has access to the unique links of each poll participant. Click on the 3 dots on a specific voter line in the posted poll and the context menu will provide the option to copy the link. Click the menu item and the link will be copied to your PC clipboard. Now you can paste it in another tool for sharing: email, chat, etc.
Note! This functionality is security sensitive, because the unique link identifies a specific poll voter. Make sure that you are sharing each link only with the correct participant over a secure channel and only do that if the default SignSpace sharing mechanisms do not work.