When Microsoft To-Do you try to sign in to with a Work Account and see the error message:
"Sorry, there's an issue signing you in right now. Please try again and contact support if the problem persists.", alongside an error code, such as:
or something similar, please try the following:
go to Windows Settings > Update & Security > Check for Windows Updates
try rebooting the PC or Mobile device
After that, try to sign in to Microsoft To-Do again. In most cases this should help solve the problem. In case the error keeps happening after that, please send us a message here.