Cannot access restApiId & restApiRootResourceId for cross stack reference in serverless yml - aws-cloudformation

Question

Since I had an issue of 200 resource error, I found a way of using cross stack reference by dividing into different services. I managed to do that by using the cross-stack reference. The issue is I cannot give the restApiId & restApiRootResourceId dynamically. Right now, am statically setting ids into the service-2.
Basically the service-1 looks like,
provider:
name: aws
runtime: nodejs8.10
apiGateway:
restApiId:
Ref: ApiGatewayRestApi
restApiResources:
Fn::GetAtt:
- ApiGatewayRestApi
- RootResourceId
custom:
stage: "${opt:stage, self:provider.stage}"
resources:
Resources:
ApiGatewayRestApi:
Type: AWS::ApiGateway::RestApi
Properties:
Name: ${self:service}-${self:custom.stage}-1
Outputs:
ApiGatewayRestApiId:
Value:
Ref: ApiGatewayRestApi
Export:
Name: ApiGatewayRestApi-restApiId
ApiGatewayRestApiRootResourceId:
Value:
Fn::GetAtt:
- ApiGatewayRestApi
- RootResourceId
Export:
Name: ApiGatewayRestApi-rootResourceId
And the service-2 looks like this,
provider:
name: aws
runtime: nodejs8.10
apiGateway-shared:
restApiId:
'Fn::ImportValue': ApiGatewayRestApi-restApiId
restApiRootResourceId:
'Fn::ImportValue': ApiGatewayRestApi-rootResourceId
As the above service-2 config, I cannot reference the Ids.
FYI: Both services are in different files.
So How what's wrong with this approach?

Answer 1

Serverless has special syntax on how to access stack output variables: {cf:stackName.outputKey}.
Note that using the Fn::ImportValue would work inside the resources section.