Unable to deploy via SAM. Getting error "Plugin 'ServerlessAppPlugin' raised an exception: AWS Region cannot be found"

[afs25]

Hi, I'm trying to deploy SAR-Lambda-Janitor via a SAM template. I've added it to the Resources section of my SAM template:

Resources:
  SarLambdaJanitor:
    Type: AWS::Serverless::Application
    Properties:
      Location:
        ApplicationId: arn:aws:serverlessrepo:us-east-1:374852340823:applications/lambda-janitor
        SemanticVersion: 1.5.0
      Parameters:
        VersionsToKeep: 3

However, when I run: $ sam build --debug -t ./template.yaml

I am seeing the error: Plugin 'ServerlessAppPlugin' raised an exception: AWS Region cannot be found

I am not sure how to solve this. Any help would be much appreciated. Thank you!