From my Family manager account, I have resent the invitation two times. Still the Join Your Family link in both links only open up a blank webpage.
Hello! @Mom&Dad
Welcome to the LastPass Community.
We truly apologize for the problem, please ask your son to open the invitation link from another browser or using an incognito window.
Also cleaning the browser could be a good option.
Please let me know if you need additional help.
Greetings!
Verlaine | Customer Care
Thank you for your quick response and suggestion. Opening an incognito window and pasting the join link worked perfectly.