What do Knight Online OTP errors mean?
| Error | What it means | What to do |
|---|---|---|
| OTP is not active | OTP isn't enabled on your account. | Set it up on NTTGame's OTP page. The new servers that opened in 2022 only let OTP-enabled accounts in. |
| Error! OTP Login Error. TimeSync is required | The app generating your code is out of sync with the server clock. | Set your phone's date and time to automatic, run the app's time sync if it has one, then try a new code. |
| Error! OTP Number is incorrect | The code is wrong or has expired. | Type it again; if it's about to expire, wait for the next one. |
| Error! OTP Number can't be reused | You entered the same code twice. | Wait for a new code and use that. |
| Error! OTP Login failed with unknown issue. Please contact customer service | The game doesn't give a reason. | Open a ticket on NTTGame's support site and attach a screenshot of the error. |
"OTP is not active" shows up on the login screen; the other four are the game's own error texts.
Can't join a new server: reasons other than OTP
If your OTP is fine and you still can't get in, check the message the game shows:
| Message | Meaning |
|---|---|
| Server is full now. Please try later. Thank you. | The server is full. Common on launch days; try again later. |
| That Nation cannot be selected to ensure populations are balanced. | This nation is closed for now to keep populations even; pick the other one or wait until it reopens. |
| You must delete all your characters in this nation if you wish to create a character in the opposite nation. | To make a character in the other nation on the same server, you have to delete all your characters in this one first. |
| You cannot create anymore characters. | You've hit the character limit on this server. |
| Selected server and the nation do not match. | When transferring, your nation on the target server doesn't match the character you're moving. |
Resetting OTP or changing phones
If you changed phones or deleted the code app, the old codes won't come through anymore. If you can't manage it on the OTP page, open a ticket on NTTGame's support site and have the details ready that prove the account is yours. Never share your OTP code or password; support won't ask you for an OTP code.
What has changed in ICS and OTP? Update history
| Date | Change |
|---|---|
| June 20, 2022 | ICS phone number changes reopened from June 20 to September 30, 2022 through a support ticket (ICS/OTP category). Players who didn't know their registered number got no help; the masked number was visible on the ICS site. |
| October–November 2022 | Pre-registering and registering on the new servers required an active ICS/OTP. The phone number used for new-server registration didn't have to match the ICS number. |
| December 19, 2025 | The ICS registration process was updated and NTTGame put the new steps in its ICS registration guide. |
The 2022 number change was a limited window. If your phone changed, open a support ticket now to find out the current terms.
FAQ
I get an OTP error when joining Zero. What do I do?
Check the exact wording and follow the fix in the table above. The most common causes are a drifting phone clock (TimeSync) and OTP not being enabled on the account.
Can you play without OTP?
The new servers that opened in 2022 only let OTP-enabled accounts in. If a new server opens, the requirements will be in the announcement; the 2022 timeline is in the new server guide.
Why does my OTP code keep coming up wrong?
Codes are valid for a short time and depend on your phone's clock. If the time isn't automatic the codes drift; fix the clock first, then try a new code.
Does an OTP error mean I'm banned?
No. An OTP error is about the login check. A closed account gets a different message; see the banned account guide.
Share your experience