Unable to login to older Modelers

Hi, We have a project on 4.8.10. We want to upgrade to 5 until we get to version 8, however we cannot login to version 4.8.10 or version 5.21.9.   we get the error attached, no matter which network or machine (work or personal), no proxy server either. How can we continue to upgrade while being unable to login and do the wizard?  
1 answers

You can work on your model offline.

And upgrade to newer versions by opening the local file in a newer version..

But, you cannot commit between steps. 


Possibly the endpoint for authentication has changed which causes the error. Which isn't really strange, since 4.8.10 was released waaay before I left Mendix. Believe me, that's a while 🙃