If the WHM returns the following error while creating new account on WHM.

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Account Creation Status: failed (Unable to add user username)
Unable to add user username
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Check the cPanel error log and you can find some logs similar like below

vipw lockfile (/etc/ptmp) is present.
vipw lockfile (/etc/ptmp) is present.


Solution: See if the lock file /etc/ptmp is present; if so, remove it.