In SubTotal Pro 22.214.171.124 on Windows PC - How to set the start day of the work week when inserting the due date Invoices in the calendar drop-down list starts on "Sunday" instead of "Monday". It's fine in the Windows system calendar and on the mobile application.
I will fix this with the next update.
In the future, please send me a mail for reporting bugs in SubTotal - this forums is for the app WorkingHours - thanks! 🙂