I recently raised a ticket to ask for help with Error 900.
For those that don't know, there's a problem with linking multiple accounts related to YT from what it seems.
There's hundreds of tickets for support and posts in the SLOBS blog about this issue, and the only way to get over it is to ask for help with the support team, which involves waiting for them to have time to solve it, which then translates to time differences, suspended streams, missed data, etc.
The solution SLOBS offers in forums to make an account as "Primary" is the following:
To change the primary account, you would need to unlink all accounts from the account in your account settings.
After that is done, log out of all things streamlabs, then log back in on the account that you want to be the primary account.
Once done, you can then go into your account settings then link any secondary accounts that you want to have linked.
Sadly, this doesn't work with Error 900.
You can't unlink "secondary" platforms due to this.
If there was a way to just change the PRIMARY platform in the settings, like a Button or selectable list, WITHOUT having to log out and log in with multiple accounts, this whole issue of error 900 would be handled by the end user, not support.
Now, I know that it may not be as easy as just coding the button, I imagine that if the "Error 900" is related to Youtube being the primary platform, it may be something related to the first time YT enters SLOBS and flags itself as primary without asking the user, forcing its way to there.
Maybe error 900 could be related to the "flag" system (the way SLOBS identifies which platform is the primary one), and when youtube "forces" its way to there, the "primary flag" on the "Twitch" platform was not cleaned or reset, so its still marked as primary too, and that's the reason why you can't unlink it even tho it appears to be a secondary platform.
Hope this helps in the future in any way, love the platform guys.