A year old thread talked about this, and the problem being the cert. I tried converting my token signing cert to PEM and uploading it, but this hasn't helped. I tried a lot of different formats, but none seem to work.
How do I go about troubleshooting this? I can't find any logging on the Zoho side of things for this, and my ADFS server shows nothing wrong (as it happily accepts the incoming requests and does the auth and then redirects back).
Any suggestions are welcome :)