I faced the same issue. I fixed this issue using these 2 solutions Solution 1: Update your device OS and Developer then try again the enrollment process. Solution 2: Try on different devices (I tried on different devices with the same Apple ID(If still exists then try it on more devices)). In my case second solution is works. I enroll 3-4 accounts using second solution.

I faced the same issue and I tried the same Apple ID on a different system(If still exists then try it on more devices). The issue is fixed. I hope it will help you. For more info watch this video(https://youtu.be/L6yptzaQNaE). In this video I suggest 2 solutions.