The way you have it setup it is looking for keys of mg.opie.app and MY_MAILGUN_PRIVATE_API_KEY in your .env file. You'll want to set these back to default and then set the values in your .env file.
So set the config back to:
'mailgun' => [
'domain' => env('MAILGUN_DOMAIN'),
'secret' => env('MAILGUN_SECRET'),
'endpoint' => env('MAILGUN_ENDPOINT', 'api.mailgun.net'),
],
And then in your .env file use:
MAIL_DRIVER=mailgun
MAILGUN_DOMAIN=mg.opie.app
MAILGUN_SECRET=MY_MAILGUN_PRIVATE_API_KEY
If you did want to hardcode them into your config file you could do it this way:
'mailgun' => [
'domain' => 'mg.opie.app',
'secret' => 'MY_MAILGUN_PRIVATE_API_KEY',
'endpoint' => env('MAILGUN_ENDPOINT', 'api.mailgun.net'),
],
or this way if you wanted to hardcode them with the ability to still override them in your .env file.
'mailgun' => [
'domain' => env('MAILGUN_DOMAIN', 'mg.opie.app'),
'secret' => env('MAILGUN_SECRET', 'MY_MAILGUN_PRIVATE_API_KEY'),
'endpoint' => env('MAILGUN_ENDPOINT', 'api.mailgun.net'),
],