Where i can change the email invoice subjet string "Invoice"

When you get a blank (second) page in the invoice pdf:

resources/views/layouts/invoice.blade.php

<div class="wrapper" style="margin-left: 0; page-break-after: avoid;">

Hello, if this issue is still an issue I found a solution. I searched in code where can you find the subject. 

In Laravel Mail Message you have to add function subject.

https://laravel.com/api/5.7/Illuminate/Notifications/Messages/MailMessage.html

Then in /app/Notifications/Income/Invoice.php add to function toMail() this line,

$message->subject('YOUR STRING HERE');

Hope I helped somebody.