Until June, German payments company Wirecard AG was a hot growth story that had shaken off allegations of accounting fraud. Then came the admission that about $2 billion of company funds had gone missing. The scandal led to the resignation and arrest of the company’s former Chief Executive Officer Markus Braun, and threatens to ensnare more executives, banking officials, auditors and even regulators. The broad impact of Wirecard’s potential demise is rattling Germany’s financial industry.