To make sure that you have the correct WebLink code, run report A8010 and select the appropriate Online Volunteer Application. The report will give you the correct WebLink URL. I like having the output type of this report set to PDF, so I can click on the link to test. As well, you can copy the link from the PDF file when ready.
You should be also able to use the form from the following location: People tab, Volunteers, and then Volunteer Request.
Blessings,
Mark Lindsley
Business Analyst, Product Management