Are you trying to recreate a contract? For that you only needed to do the login, you can just close that tab and return to Fiddler.
And what kind of OAuth Token.
Is the field for the token filled or empty?
If it is empty try to redo the login into your IO account in a different Web Browser.
If it is filled you only need to insert the contract json you want to recreate.
You have to redo the IO login in another browser, I suggest to use Firefox.
If English is difficult for you you can try to translate the text of the editor and of the topic with this site. I frequently use it and it seems to be better than Google Translate:
I tried to use opera and chrome
Opera and Chrome use the same engine, Firefox is different. Might be worth to try.
where the OAuth Token will be written. ?
I currently run out of ideas what is the issue here. To make sure IO did not block you people manually by account, would someone let me log into their game on Epic Games and let me try to create a contract? Volunteers please send me a PM.
In the left field, below “OAuth Token”. That happens automatically after the login.
Just got home and tested the tool – still works for me!
I hate to be that guy but maybe making 10-20 target contracts isn’t the way to go 
Tread lightly.
Now that is weird, one less explanation what is going on.
I would suggest generally it is worth a try to fully uninstall fiddler (including drivers) and reinstall it again. When I did that I did not need to reinstall the mod tool but just in case make backups of your Contract folder first.
I actually started working on a little appendix for the Contract Creation Guide. Especially for mods:
Any more inputs always welcome!
Contract creation for Mods
Kill conditions:
Use Any/Any or weapons found in the map you’ve chosen for the contract. For example: It’s frustrating for someone who just has H3 to play a Dubai contract only to realise that the Striker isn’t available. Same goes for disguises.
Targets:
Don’t use too many targets. It’s fun to chose all the agents in Berlin as this gives the contract a twist (kill them before they exit the map or you won’t be able to finish this contract). But more targets doesn’t mean more fun or higher difficulty. It’s usually just annoying. → refer to the target count in the original Contract Creation Guide.
Complications:
Same rules/suggestions apply like in regular contract creation. You could shorten the time limit to force the player into a sniper contract (as you can’t tag your targets too far away). But as with every contract make sure to play and test it a few times to see if it works.
Easter Eggs:
If you’re using weapons/exits/disguises (looking at you, New York) that require certain actions to appear, make sure to at least leave a hint in your briefing.
@CybraxCyberspace reading this:
lol you are mean @ColdDayInHell I am not laughing at this, I think it’s very good.
I see no problem with a 10 target contract if it makes sense and/or is reasonable or cool but they should be rare.
I kinda would never go over 6 for myself, i think its the magic number that allows for some extra special stuff.
Again i think this is great info I am just the real ballbuster contract guy lol and I always will be also i always leave hints / instructions that help to complete the contract.
It’s never enough!
and I’m just teasing.
Most 10 target contracts would suck.
Your axe one was actually brilliant so I’ll give that one a pass. 
Too bad the server kicked me off mid-run LOL.
Edit : yes you give hints. I hate required exit contracts that aren’t determined in the briefing. It’s like okay let me waste time killing everyone just to see how I can leave.
All credit to @linux_penguin on that one, I just remade and modified it.
Ohhh yeah. Fack, he makes killer contracts. That might be the most innovative contract I’ve played all year.
What do you mean by this?
Also thanks for the kind words!