Need help in Dimensions value

I am not sure what needs to go in for Value: under dimensions for a latency alarm for AWS::Serverless::API

Ive tried Value: !Ref ApiGatewayApi and !Ref ApiGatewayApi.stage and !Ref ApiGatewayApi.Deployment
and tried some combinations of !GetAtt but that failed to deploy as I wasn't sure what to put for parameters but Ref didn't

CountAlarmApiGateway:
    Type: 'AWS::CloudWatch::Alarm'
    Properties:
        AlarmDescription: Time from receiving and returning client request
        ComparisonOperator: LessThanThreshold
        Namespace: AWS/ApiGateway
        Threshold: '1'
        MetricName: Latency
        DatapointsToAlarm: 1
        EvaluationPeriods: 1
        InsufficientDataActions: Insufficient Data
        Period: '60'
        Dimensions:
            - Name: ApiName
              Value: !Ref ApiGatewayApi
        TreatMissingData: missing
        Statistic: Average

code does deploy in CloudFormation but I don't have the actual ApiGateway name under value that I am looking for What I'm looking for is stackname-ApiGatewayName