It seems like non-refundable portion is the sum of "Check-in fee" and "Service fee", and in case of German flights it's just a "Check-In" fee. Most likely this non-refundable part is also deductable in case of "Pegasus Flex", according to some reddits. I have no idea why they make this information is so hidden/unclear. I have doubts if they earn something on such games... at least I preferred to chose another airline with clearer refund policies to get my flex ticket.