Please disable third-party plugins and customizations (if there are any) and check if this issue persists. If you use a caching plugin, ensure that caching is disabled for logged-in users.
Also, please refresh the permalink structure in Settings/Permalinks (choose any structure with %postname% if the default one is selected) and check if this issue persists.
Please ensure you have not overwritten the Add Listing template with an empty value in HivePress > Templates.
If you enabled direct vendor registration, then this URL should be available, but there’s no page for it in WordPress/Pages, this is a static template generated by HivePress. You can override it if required using the Templates feature Overview | HivePress Templates - YouTube.