Hmm, the only thing that comes to mind - is the order of the tabs in your work book?
With the way you’ve set your IF trigger - the tab with the calculations in need to be in the very left most tab; (Or alternatively add [Tab Name]! before the F2 cell reference.
If the problem is IFTTT side, that might be the cause.
If you change the date in B2 to the day before your last salary, does cell D2 update?
Final thought - in your spreadsheet settings - is your “Location” Set to UK? I just nipped back into my test sheet and I had the location as US Once I changed it, the formula picked up again.
Let me know if any of those work?