I don't know what https://sitemanager.itunes.apple.com/ is - I'm told I can't log into it with my Apple ID - but you should be submitting your podcast at http://podcastsconnect.apple.com . However when I tried to validate your feed there I was told it could not read the feed.
I cannot find anything wrong with the feed as such - it validates in several feed validators and works perfectly well in iTunes when subscribing manually. The image appears to be OK. However the URL for your media file begins with https and though these days this seems not to be a problem with the Store it's inadvisable: substituting http will work.
The file is plainly just a test as it's only a few seconds long and is a single moving image; this is likely to be rejected as they don't like tests - they need to be able to check what your podcast is really like. Furthermore the server your file is on does not support byte range requests - the method used by iPhones to download the files, and which is mandatory. You will need to find another server. Incidentally your filename has a space in it,and though the feed has correctly handled this by substituting the code %20 (as spaces are not allowed in a URL) you would do better to remove it.
Incidentally your feed has no 'itunes:subtitle' or 'itunes:summary' tags for your episode and it's advisable to have these.