The phrase "not only fails" is correct and can be used in written English.
It is commonly used to introduce a contrast or a surprising outcome. Example: Not only did he fail the exam, but he also failed to study for it.
Prohibition not only fails to stop drinking, but also worsens the horrific consequences of alcohol abuse.
Hamas will now be able to claim that diplomacy not only fails to bring results, it brings national humiliation.
The assertion that Brazil's judiciary is both corrupt and inefficient not only fails to portray reality, but is flagrantly irresponsible.
The policy not only fails to make the Israeli public more secure; it arouses more anti-Israel violence.
But he not only fails at that job but realises he has to biff off when her fiancé shows up.
Goya obliges the king's request for a portrait, but his depiction not only fails to flatter but reflects a terrible darkness and grotesqueness.
And the result is a plan that not only fails to deliver help where it's most needed, but is likely to fail as an economic measure.
As Darwin knew, when individual and group interests diverge, competition not only fails to promote the common good, it also actively undermines it.
The official poverty measure not only fails to include the effect of the earned-income tax credit or food stamps — the biggest anti-poverty tools the government has.
It not only fails to question Islam's foundation myths but augments the myth-making by excluding evidence that might embarrass the Saudi royal family.
If the left continue to back a Labour party that not only fails to represent their views, but actively opposes them, then that will never change.
