If you have a list of saved prospects, here is the correct way to create a supported URL for Growth-X.
First, please check this article from SalesNavigator showing step by step instructions for creating lists.
Please note, just saving a lead to 'my saved leads' will not be supported as there are no filters in the search criteria. The URL should NOT begin in this format: https://www.linkedin.com/sales/search/people/list/saved-leads?
To create a supported URL, you must create an actual 'lead list' and add it to the 'Custom Lists' filter.
If you already saved the leads previous, you must select all and save to a 'lead list'.
The last step is adding the saved list to the 'Custom Lists' filter. Click on it and select the lead list.