Podcasts connect "Can't parse your feed" I'm trying to submit a podcast to Podcasts Connect and I get the error

Can’t parse your feed.

With a status of

Failed Validation

This is my feed. I've used multiple rss validators (Here's the list)

Podba.se
Castfeed validator
W3C rss validator

Among others. Every validator says that my rss is good or has nothing bigger than a few warnings, but whenever the Apple validator at Podcasts Connect gives this error I mentioned saying it cant parse the feed, but not any further description. Any Idea of what could my problem be or where is my mistake?
UPDATE: Just as a test I tried to submit it to Spotify and it didn't worked.
Ok so after a lot of trial and error I found what was causing the trouble.
My feed had this line at the very begining:
standalone=&quot;yes&quot;

Inside the &lt;?xml ?&gt; declaration.
Removing that from the feed fixed it for both Apple Podcasts and Spotify.