AWS Sum Metrics

Hi - probably a simple answer (hopefully!) but I am trying to use the AWS SUM function to add 3 different metrics from cloudwatch.

SUM(REMOVE_EMPTY(SEARCH(’{AWS/FSx,FileSystemId} MetricName=“DataReadOperations”’, ‘Average’, 300))) + (REMOVE_EMPTY(SEARCH(’{AWS/FSx,FileSystemId} MetricName=“DataWriteOperations”’, ‘Average’, 300))) + (REMOVE_EMPTY(SEARCH(’{AWS/FSx,FileSystemId} MetricName=“MetadataOperations”’, ‘Average’, 300)))

The sum function works with 2 metrics but not with 3 (and it fails within cloudwatch as well). If anyone could point me in the right direction it would be appreciated.