Using the WORKDAY function, I notices that it only works for positive values, for negative values it returns an error. I contacted the Support Team and they said: "Thank you for providing the URL and the screenshot. 🌤️ This was very helpful for our team to investigate the issue with the WORKDAY function when using negative values. Our team has found that the reason why negative values do not work is that the WORKDAY function can only return a date object corresponding to the number of working days after the start_date. Returning working days before the start_date would be a feature request. My team and I tried to create a workaround, but we have yet to find one." So here I am writing a feature request. I hope that they solve that problem soon.