Calling me a troll?
https://prnt.sc/gskwi1 (just in case picture is broken on the forums)
That line alone translate that you tried streaming directly to mixer and it worked so you feel it should not be an issue with joicaster. The rest of your post is irrelavent after saying that one line.
Yes you can stream directly to mixer with no problems but if a restreaming service like joicaster or restream.io don't work then it's a problem on their end and not mixer.
Now back to actually trying to help you did you bother to take mixer off and put it back into your profile on joicaster? I find it very hard to believe you even use restream.io cause i know many casters that stream DAILY on twitch and mixer and they have had no problems. My thing is with your problem is you are changing your key on mixer which in a way invalidates your connection with joicaster and probally restream. Now again I have no clue how their backend system works but with common sense you linked your account with those services knowing you had a particular key. BEFORE YOU SAY SOMETHING READ ON!
When you click on the button to sign into mixer to sync it with joicaster, restream or practically any website with some type of authentifaction....If you do any MAJOR change to your account there is a possibility you need to resync your account! All it really does when you do that is it puts in what your stream key was at the time you did the sync. NOW THIS IS WHERE I DON'T KNOW THE BACKEND KICK IN
If the devs of the website coded correctly you'd think that the system makes sure the key is still the same so if you were to change your key it auto changes it for you. It seems that is not the case! Because you changed your key on mixers end then joicaster is not going to see the new key cause it's locked in on the old key. If you remove your mixer with joicaster and resync then it will fix itself. Same with restream if you are actually using it. Now here is the last thing I urge you to do and i will break it down!
Joicaster - Take mixer off and put it back on for it to see your new key. Go live and see if it worked. If not go to step 2
Take mixer off restream.io and put it back on. Go live and see if it worked. If not go to step 3
Make sure you are using the latest version of OBS which as i type this message it's 20.0.1. After verifying you are using that version then try to go live with just mixer only! If you can go live then there is some corruption in your restream and joicaster account. If you can't go live then open a ticket at mixer.com/contact
Optional Step 4
Download and use XSplit - https://www.xsplit.com and try steps 1 - 3 again with xsplit. There have been rare reports that xsplit works in the weirdest way cause joicaster and restream.io should work no matter what program you use.
Overall computers are weird when it comes to problems like this. Something simple can be complicated for no reason.