Shared photostream wont invite people

i have created a shared phototstream and invited a bunch of people. Some got the invitation and accepted but others didnt even recieve the invitation. I made sure they had it turned on in settings and i tried resending the invitation but they still didnt get it. For one person i tried sending it to their phone number and their email and it still woudn't work. On the "people" tab on the stream, everyone who didn't get the invitation says "invited" but they didn't get the invitation. What is wrong here?

thanks