Using vars in EFS/fileSystemConfig fails

I’m attempting to add an EFS mount config to an existing serverless config and it doesn’t seem to allow the use of variables in the EFS access point ARN. I’m trying to do something like this:


However it fails with the following error:

Configuration error at 'functions.hello.fileSystemConfig.arn': should match pattern "^arn:aws[a-zA-Z-]*:elasticfilesystem:[a-z]{2}((-gov)|(-iso(b?)))?-[a-z]+-[1-9]{1}:[0-9]{12}:access-point/fsap-[a-f0-9]{17}$"

Is it really not possible to use vars in an EFS access point ARN?