Where should the ecommerce-config.yml saved?

I want to activate tutor’s ecommerce plugin, and it said that I should modify some config, like setting up the paypal’s client id and lastly I need to load that config with:
tutor config save --set "ECOMMERCE_PAYMENT_PROCESSORS=$(cat ecommerce-config.yml)"

My question is, where should that .yml config be saved?

because when I just run the tutor dev start I will get this error message