It looks like you haven't actually deployed the code. Once deployed a free Mailgun account is created for you behind the scenes and assigned to your app. To test locally you need to create a Mailgun account and follow instructions from the "Extra optional step" section.
It looks like you haven't actually deployed the code. Once deployed a free Mailgun account is created for you behind the scenes and assigned to your app. To test locally you need to create a Mailgun account and follow instructions from the "Extra optional step" section.
BR, Sergey