Amazon Web Services : Error - The security token included in the request is invalid

I have a developer authenticated identity set for Amazon Cognito us in my iOS app

I have followed the tutorial in the documentation: Using Developer Authenticated Identities

My backend is able to generate tokens and get identityIds with no problem. And I am able to initialize cognito in my iOS app as instructed. But I upon making a dynamoDb request I get the error

The security token included in the request is invalid

Cognito initialization Code:

 MyIdentityProvider *identityProvider = [MyIdentityProvider new];
[identityProvider setIdentityPoolId:COGNITO_POOL_ID];

AWSCognitoCredentialsProvider *credentialsProvider  = [[AWSCognitoCredentialsProvider alloc]
                                                       initWithRegionType:AWSRegionUSEast1
                                                       identityProvider:identityProvider
                                                       unauthRoleArn:nil
                                                       authRoleArn:COGNITO_ROLE_AUTH];




AWSServiceConfiguration *configuration = [AWSServiceConfiguration configurationWithRegion:AWSRegionUSEast1
                                                                      credentialsProvider:credentialsProvider];

[AWSServiceManager defaultServiceManager].defaultServiceConfiguration = configuration;





[[credentialsProvider getIdentityId] continueWithSuccessBlock:^id(BFTask *task){

 //In here I can see that everything is ok.
 //I have a token and cognitoId
 //But despite this, when I make requests I get "The security token included in the request is  invalid"

 return nil;
}];

Does anyone know what I might be doing wrong ?