I was able to create a remote with backblaze as well.
Unfortunately, I got no more answer from pcloud about this issue.
I really would like to buy for 'pcloud premium plus' because of its good Linux integration but rclone functionality is a must have for me. 
it is really strange that every time i create a pcloud remote, i am successful.
on windows, on android, on linux seedbox.
whereas every time, your attempts fail
i assure you that i do not profit financially from donations.
@hoxi would you be willing to lend me your credentials so I can investigate the problem? Maybe on the new account you just created which presumably won't have anything in? If so then PM them to me. If not, no worries, I'm sure we'll figure it out eventually!
I totally agree, I don't get it either.
Therefore, it would really help if pcloud could send us more information from their log-files.
I do not think that I am doing something wrong because I am able to connect to many other cloud accounts. I have tried it with different hardware, different rclone versions, 3 different operating systems, a different internet access and even a different pcloud account and I have got always the same error message.
That's really strange! 
Good idea, we can try this.
Jumping into the pool to help - it really appears to be localised to your specific setup. Since you switched systems - and had the same result - does that not point to something farther upstream (router, switch, firewall configuration)? We are using Rclone and pCloud now without issue - after getting passed the 2FA. One other long shot but worth mentioning is that pCloud is opening the European-based data centres in July for existing users. You may be able to setup an account today and point towards the EU data centres. Worth a try if you have not already.
Thank you very much for trying to help.
Nick has already figured it out.
The reason seems to be a different api-interface behavior of pcloud in my region (not documented yet).
This behavior could be linked to their new EU data centres because that's my region.
Glad to hear that is is solved for you. It makes sense that it was something farther upstream between you and the pCloud servers. We are EU, too - and looking forward to moving our data back to Europe! For existing users, there is supposed to be an option to do that this month. That link explains this is news as of yesterday/today. Kudos to the Rclone team as well for sticking with it to solve it.
Yes, now everything makes much more sense.
I would wait with the migration until pcloud has ironed out all issues. though.
But it could also be that existing api-connections show no problems or what so ever.
I think I've fixed this here - can you have a go and report back? The API hostname is returned in the oauth callback apparently so if we use that then everything seems to work OK. This doesn't appear to be documented at pcloud yet though!
v1.52.2-194-g313b3c1c-fix-pcloud-oauth-beta on branch fix-pcloud-oauth (uploaded in 15-30 mins)
@Jineu do you know if there will be docs for the oauth extension that pCloud is using - returning the hostname in the oauth callback?
This isn't unprecedented - Citrix Sharefile does it for example - it would be nice to see some docs on it to see if I implemented it right!
Thanks
I can confirm, everything works perfect so far.
I have configured sucessfully a new remote configuration with my pcloud account and a headless connection worked as well.
Thanks a lot! 
Support of pcloud is waiting for feedback from my side. In case it's missing I can tell them that they should update their official developer documentation.
Unfortunately not! The only docs we could find are on the pCloud developer page. Their customer service has been good. When in doubt, give them a shout! It will help them get more users, so it's in their interest to assist.
I've dropped pCloud a note about the situation - I'll update the thread with what I found out.
I've merged this fix to master now which means it will be in the latest beta in 15-30 mins and released in v1.52.3 or v1.53 whichever comes first!
Are you using the beta linked above?