Hello, I haven’t been able to open my Home Assistant cloud link for a few days. the certificate will not be accepted. before that it always worked. seems like it has expired. iOS says “not trusted”. what can I do there?
Did you try other browsers on other devices? What iOS version on you on? What device?
Did you try turning it off and on? 
Bit of debugging on your own end goes a long way:
Thank you for your reply.
I have different nabu Casa Accounts (for me, my parents, friends etc.). I can access all accounts via nabu Casa cloud accept of one. So it can‘t be a issue of my iOS. I can access this one account with my Notebook and chrome. On my iOS device I can’t… Any idea?
How are you connecting on your iOS device? Safari? HA App? Magic?
If you can access the site on other devices then there is no problem with the certificate from Nabu.
Also iOS is the operating software, its not the thing that connects to Nabu but that will be your browser or app. Sounds like a cache issue and there are several steps you can take to try and fix it. First one would be to clear the cache of your browser. 2nd step would be to check if your device has the correct time and date.
Maybe some iOS users here have some other tips.