Surging downloads and use of its two-year-old digital banking apps are boosting the confidence of Indonesia's top lender Bank Mandiri, as fintech players try to retain existing customers while looking for more among the country's large unbanked population. All [regional tech giants and fintech startups] want a slice of the lucrative market in Indonesia, where mobile phone penetration is high but where 80% of the population is either unbanked or underbanked.