An error occurred while saving the commentJose Rosario commented
I found a weird workaround that worked for my case where I'm simply linking to other Planner boards. For example, I start with,
Obviously, the "https://" prefix is already provided by Planner. I substituted my private info. But it complains when I give it the above, saying, "Please enter a valid url", leaving the Save button disabled. When I switch it to this:
....now the Planner error goes away and the Save button becomes enabled. If I click the link in the saved Planner task now, it opens the right board up and the URL I see in the address bar ends up being:
Notice the ampersands are put back in place and everything works! However, this workaround where I switch an ampersand for a plus sign does not render every URL valid. Although Planner will allow these URLs to save and this worked for links to other Planner boards, some other manipulated URLs to other sites fail.