So I talked to my hosting provider and they help me to fix the problem / find out what the problem is.

Could this be right ?

+--Below that they said +++

Hello,

Thank you for your patience!

We would like to inform you that we have checked our error logs and it seems your application doesn't enough resources.

We increased temporary the Input/Output usage resources and CPU for your account temporary and we were able to upload the test video for your website.

You can confirm it via the following URL:

( Yes it was working )

Considering this we recommend you upgrade your current package Starter Package - sitename  to an Enterprise Shared package or to an Enterprise Cloud Shared package.

More information about each of them you can find via URLs provided below:

Link here 

Link here 

Please, do not hesitate to contact us again if we could be of any further assistance!

Best Regards,