Update(change) user-defined metadata of the AWS S3 object with iOS SDK

Can anybody help with that?

I tried to use AWSS3ReplicateObjectRequest setting bucket, key and replicateSource properties to point the same existing S3 file, setting metadataDirective to AWSS3MetadataDirectiveReplace and assigning new user-defined metadata. In that case I have error:

Error Domain=com.amazonaws.AWSGeneralErrorDomain Code=3 "The operation
couldn’t be completed. (com.amazonaws.AWSGeneralErrorDomain error 3.)"
UserInfo=0x7ae60ef0 {Message=The request signature we calculated does not
match the signature you provided. Check your key and signing method. ... 

Have I missed something here? (AWS iOS SDK v2.2.4)