Discourse has magic embedding we call onebox, so you don’t need to paste their embed code at all, just add your playlist URL on a single line like
https://www.mixcloud.com/wannabedj48570385/sharingmylamemixes/
And it becomes
Now if you really want the embed code to work you need to fiddle with the site setting
Testing embed code:
Looks like it works fine after adding it to the allowed iframes site setting.