I put out an in-game notification about this. I'm trying to fix it right now.

I did manage to fix it so that you can load the front page. All saves fail to load though. This is because there's a separate server that hosts save data, I was only able to fix it for the main server (powdertoy.co.uk)

I'll keep looking for a solution. I can avoid a client update if I'm able to get the save hosting server "fixed". But also, the tpt client is definitely bugged, it should be able to load the website but is rejecting the ssl cert.

Edit: Android version 1.13 released to permanently fix the issue

This has been fixed now. Please update to version 1.13. This version was just released, so it may take a bit to get to your phone, but if you go to the Play Store now, you should be able to update.

Please see this thread for more details:
https://powdertoy.co.uk/Discussions/Thread/View.html?Thread=25549

If you are on the latest version (1.14) and still getting this error, there's nothing I can do to fix it right now.