Operating CF from Nobrie

Hello Tutor,

I have a question related to question 36 Mock Exam 2 in BPP revision kit 2022 – Preparing Operating CF for a company Nobrie. There is one line for interest received. I never encountered such line before in textbook or lecture. But as it was listed, I tried to answer as I remember interest received can be classified as operating or investing CFs. But it was wrong: as per solution, they deleted that line without any explanation. I got confused. I suppose it was a trap? And can you please give me any tips on how I can overcome such trap in exam?

Thank you tutor!