Yes, there are several legal considerations to keep in mind when building a payment processing app:
Regulatory Compliance. Different countries have specific regulations related to electronic transactions and data privacy. In the U.S., for example, one must comply with the PCI DSS. In Europe, there's the GDPR law concerning data protection and privacy.
AML and KYC Policies. Ensure that your app has mechanisms to prevent money laundering and verifies the identity of users to mitigate fraud.
Consumer Protection Laws. They protect consumers' rights, especially regarding refunds, chargebacks, and disputes.
Licensing. Depending on the region, you might need certain licenses to operate as a payment processor.