HungryFEED can't get feed.Tradedoubler error?

I want to display an Itunes feed as an affiliate. Their program is through Tradedoubler who give the following guidance:

In order to create track-safe links, using the “RSS Feed Generator”, you need to add, in front of your selected URL, our click URL.

This will lead you to the following general format:
https://clk.tradedoubler.com/click?p=23708&a=2370130&url=%5BRSS_FEED_ENCODED_URL%5D
where, [RSS_FEED_ENCODED_URL] is the encoded URL, which was taken from the RSS Feed Generator.

Example:
https://clk.tradedoubler.com/click?p=23708&a=2370130&url=https%3A%2F%2Fitunes.apple.com%2Fgb%2Faudiobook%2Finferno-unabridged%2Fid641363617%3Fuo%3D2

When I put just the itunes generated rss feed in it works. When I try to add the tradedoubler url to the start of the url as show in the example above I get this message:

HungryFEED can’t get feed. Don’t be mad at HungryFEED. SimplePie reported: This XML document is invalid, likely due to invalid characters. XML error: Mismatched tag at line 1, column 115

How can I fix this please?

https://www.ads-software.com/plugins/hungryfeed/