I solved this. I was trying to edit my video directly from photolibary. So, save the video to documentDirectory first, then edit worked for me.

After sending several messages, they finally replied.

Hi I'm facing the same issue. Did you find out the solution?

Hi dermantapaz, I'm facing the issue too. Did you managed to solve it?

Thank you all for the reply! I tried opening the link again this morning, and it worked! Just had to wait for several hours to reflect the changes of apple-app-site-association.

Why does every issues with 'Sign up not completed' require technical support? Are there no straight forward answers??