[Home](./index.md) > [@firebase/auth](./auth.md) > [PhoneMultiFactorSignInInfoOptions](./auth.phonemultifactorsignininfooptions.md) > [multiFactorUid](./auth.phonemultifactorsignininfooptions.multifactoruid.md) ## PhoneMultiFactorSignInInfoOptions.multiFactorUid property The uid of the second factor. One of `multiFactorHint` or `multiFactorUid` is required. Signature: ```typescript multiFactorUid?: string; ```