One Kuaimiao account, several devices
Set up Kuaimiao VPN on more than one device, confirm the account and plan limits, and give each device its own password. When a single device fails, compare the same network and the same route so the cause stays readable.
Keep the account protected
Use a password of your own and check the device rules of the plan you are on. Keep verification codes and payment details to yourself, and use a separate password on shared machines.
Install and sign in
Follow the installation prompts of your platform. Approve the system VPN permission request, then sign in with your current account. How many devices you may use depends on the plan.
Make the difficulty reproducible
Note your platform, system and app version, the network type, the exact error wording and which device failed, so the next step can be reasoned about rather than guessed.