Feed does not validate

Hello

I try to submit my first podcast to iTunes, using iTunes podcast connect. In the process, I need to validate the RSS feed, however that fails.

Using the Feed Validator W3, I get several errors reported on this feed. You can recreate this with this link:
https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Ftransmissible.eu%2Ffeed%2Fpodcast

As far as I know, I have set all settings correctly. Could you help me with some advice ?

Thanks in advance
Arnold