You also need to add the file deploy/client/.env similar to .env.example and set the NEXT_PUBLIC_EDAV_S3_SIGN_URL and NEXT_PUBLIC_EDAV_SERVER_URL variables to the URLs used for deployment. Unfortunately, unless you are using a custom domain name, these URLs will not be available until after the first deployment since Next.js does not support runtime configuration for serverless builds as of the moment of writing this template.
After you configure your AWS account:
export S3_BUCKET=<S3 Bucket for SAM packaging>
# Override SAM arguments
export SAM_ARGS='--parameter-overrides ParameterKey=CloudfrontAliases,ParameterValue=example.com'
make deployYou may also refer to example.com.sh and .env.example for customization and parameterization examples.