You just needed to add to the end the last IF block. It’s a little easier to understand what’s going on if you edit while indenting (just make sure you take the indentations out before running it).
IF(LOGIC, what happens if true, what happens if false)
Since you’re nesting IF blocks, ‘what happens if false’ has been routing you to the next IF blocks. But with the last (or most nested) IF block, you hadn’t provided a false return value.