Creating own VPN using Outline Manager and hosting on google cloud

when i’m pasting the outline manager code in to ssl window it ask for to install Docker when i press y and hit Enter it throw an error

Verifying that Docker is installed … NOT INSTALLED

Would you like to install Docker? This will run ‘curl -sS | sh’. [Y/n] y
Installing Docker … Docker installation failed, please visit ---- for instructions.
Sorry! Something went wrong. If you can’t figure this out, please copy and paste all this output into the Outline Manager screen, and send it to us, to see if we can help you.

the docker installation page is also missing plz help me how to fix it