API connector app login issue

I have two apps that I am trying to connect. I want to be able to log in to app A and have a button there that when clicked will navigate and log me in to app B. I did have this working, but for some reason it no longer is and I can’t get it going again. I have been searching for a while now to try and find some information on how to do this but have not been successful.

Problem Solved

Hi, how did you link both app together with one login?