The Independent Parliamentary Standards Authority (Ipsa) faced a backlash from MPs after saying they could claim for festive get-togethers.
MPs on all sides rejected the guidance, with one calling it "bonkers" amid a cost of living crisis.
Ipsa's chief executive Ian Todd said the body had "got the messaging wrong".
In a letter posted online, he added that some MPs had had to deal with "phone calls, e-mails and in some cases abuse as a result of our guidance".
Ipsa had initially defended its approach, saying after it was published that holding a "modest gathering" for MPs' staff was "entirely appropriate".
In his letter, Mr Todd said Ipsa had produced the guidance following requests for advice about applying the organisation's rulebook.
He added that afterwards he was contacted by numerous MPs, who "have made it clear to me that they have never made such claims in the past and have no intention of doing so in the future. I accept and respect that."
"We got the messaging wrong by allowing the impression to form that this is what MPs were wanting to do, rather than our interpretation of the discretion available under the existing rules," he added.
"We are an independent body and we make our own decisions but occasionally, like everyone, we make mistakes."
"In issuing it we also failed to recognise the public mood at a time of severe economic and financial pressures. I am sorry for that."