The shortcode will accept just the page (but the page has to actually exist). Also, what you pasted may or may not be valid (depending on the encoding relative to what you pasted). You’ve got it wrapped with curly quotes (”) which are not valid as quotes in a shortcode. So I’m not sure if that happened when you copy/pasted to the forum here or if that’s what is actually in your shortcode. You’ve also got “%5D” which is the HTML encoding for the “]” closing bracket. So double check that as well.
You don’t have to use the full URL. You can just use the page, and also ditch the quotes if necessary. So if the page slug is actually “test” that’s all you need. Just make sure it has a leading slash (i.e. “/test”).
[wpmem_form register redirect_to=/test]
OR
[wpmem_form register redirect_to=”/test”]
If you want to check to see if you’ve got a valid result, right click in the form and select your browser inspector (“Inspect” in most browsers). Look for the hidden fields in the form – you’ll see one that is name=”wpmem_reg_page” which should indicate a value for the current page. If your redirect_to shortcode attribute is valid, then you should also have one right below it that is name=”redirect_to” and a value that matches your redirect_to shortcode attribute. If you have “wpmem_reg_page” but no “redirect_to”, then either your attribute invalid, or you’re not actually getting the shortcode result in that location.