Cannot approve invite to join collaboration invite

Hi,

I'm having difficulties accepting a collaboration invite from outside of my organization. From my end, I have received the invitation email, but when I click on it I do not see any notification or option to accept the invite. On the inviter's side, they see me as "pending" on their list. 

I've already tried clearing my cache, restarting my browser and other common troubleshooting activities. The person who sent the invite has already resent twice. Please advise on how to resolve this, thanks!