The landlord is trying to get a loan against the property. In order to do this, he must prove that the leases/rents are up-to-date and that the property is being managed well to assured it as a source of payment for the new loan. The Estoppel Certificate proves that rent is coming in on time on the property. In your case, this is not true, but it doesn't do the landlord any good to say that you are behind on the rent and that he has allowed this to happen. On the other hand, he's asking you to do him a favor to support him in getting this loan. Given that you are behind, he could easily start eviction proceedings. But to sign the certificate is an effort to defraud. Make a plan to get caught up on the rent, even if it is a little bit extra each month and sign a private agreement with the landlord about that. If the arrangements are made between the two of you to clear up the arrears, perhaps that could be considered a "current" arrangement and you could sign the Estoppel in good faith.