"In November we open the jam."
Translation:A novembre apriamo la marmellata.
You don't use the personal pronoun "noi" because it is already included in "apriamo". Since "apriamo" means "we open", that would be like saying we we open. You may use "io" and "loro" instead of just "sono" in order to clarify if it isn't clear from context and you may use "lui" and "lei" to clarify, otherwise they aren't used much apparently.
It didn't take that for me either and the best I can tell is that you, like me, left an l out of marmellatta - it should have taken it and said "hey typo" because google translate figured it out (I get that it can't take if it is a completely different word), but that's my best guess. I didn't use noi (but that shouldn't matter) but I had to really analyze my answer to figure out what was different - a single l and I can't figure out how to tell when you're supposed to double and when not... or why it even matters - in spanish it changes the pronunciation, but in italian -l- -ll- and -gl- all sound EXACTLY the same to me... so I don't get it.