Get GZIP compression enabled for your call (to update the channel) and you’ll be able to read the error body response.
You can also totally remove channel_feed_enabled from your JSON as the feed is dead/removed feature, it’s just in the docs for completeness
If you call channel_feed_enabled you need channel_editor from the channel you are trying to update.
Otherwise
You need a key with channel_editor on for YOU and YOU are also an editor on the target channel.
-OR-
You need a key with channel_editor on for the channel you wish to update.
Unless you are trying to update your own personal channel, I anticipate you have the wrong owner of the key