Nubank, the world’s biggest digital bank by market value, is planning to invest $150m in Tyme Group, valuing the neobank launched in South Africa at $1.5bn and helping to finance its push into south-east Asia. The cash injection will bring Tyme into a select club of Africa-related “unicorns” — start-ups valued at above $1bn — and underline Nubank’s growing reach outside Latin America.