I understand that there's been different scams in reference to flight compensation, with people losing their money because other got it (errors with the account id, plain scams, booking for groups where only one got all the money, or the agency) and companies may be triying to prevent this. Lately I have read people complaining that Iberia says they are even but they didn't receive the money. Somebody got it instead.

And I know that the certificate is necessary under the Anti-money laundering Acts for a bunch of entities. Not sure if airlines are into that group.

In any case, it's about confirming your account to warrant that you receive your money.