I have been getting the above error for several weeks now trying to add cross posting to Mastodon.
I don’t think this is an error on my end since I’ve been able to authenticate with many other apps/clients, but if anyone has any experience with this type of thing, could you provide any tips to get this fixed? Thanks in advance.
I’m getting this same error trying to connect to my Masto.host managed instance.
Likewise, I don’t have any other issues authenticating other services.
I think this happens when some authentication info with the Mastodon server is cached and has changed. I’ve reset it to your server in Micro.blog. Can you try again and let me know if it doesn’t work?
Thank you for the prompt response. That worked straight away this time 
Howdy @manton, I have encountered the same problem as reported here. I don’t suppose you could give my account a similar nudge to see if that fixes it? (jmac@micro.blog, mastodon server masto.nyc)
I’ve also got the same problem, in my case I’m trying to connect the tjoho.mostrom.eu site with mastodonsweden.se
Have also been hit by this issue (I recently had to migrate my Mastodon instance to a different host, so the auth changed.)
Same for me, I’m trying to connect to mementomori.social. 
As best I can tell, this happens when something on the Mastodon side changes, like maybe a re-install or database upgrade?
I’ve reset the cache for mementomori.social so let me know if that works now. I think I can automatically reset it in the future when detecting this error.
Edit: Oh hold on, not it worked! Needed few retries
Close, but no cigar. Now I got bit further and saw this:
When I click the authorize button (the left purple one), I then get here:
Can it be their end?
Still seeing the original error when I try to authenticate to my Mastodon instance (thomasjpr.social) which was a new install of a previous instance.
Same here, doesn’t work connecting tjoho.mostrom.eu with mastodonsweden.se
FYI I saw something going around about Ivory having these problems too. I think a recent mastodon server release messed with how a lot of this worked.
Tried logging into an account on a different server hoping that would clear this authentication error if I then tried to log into the original. Still no dice.
If anyone is still seeing this, can you email help@micro.blog with the Mastodon server name? Often I can manually reset our cache for that server and it will start working.
