Need Help to access My Cloud private folder

1st Question:
I created 2 private folders via inviting 2 users.
admin has read and write access over those 2 said folders.
admin has a password that I can confirm that is correct. (I can use the browser interface)
I tried to map these private folders as drives.
Stuck at the Windows 10 credential as I am entering
username: admin
password: (The one I used for browser interface)
Here is the image

What should I do?=

2nd Question:
Users properties in the browser interface show 3 possible usernames:
first name
last name
Which one should I use for the windows 10 credential?


You could refer to the following link: