Dear @Ams,
Service Providers are the core solution enablers within the e-Invoicing ecosystem. The framework was intentionally designed to bring experts like you on board to address specific implementation scenarios such as the one described.
Our advice is for you to adopt an enterprise architecture approach that accommodates diverse systems and integrations. With this design, your solution can be easily adapted and reused across multiple organizations, even those operating different ERP environments, while changing just the credentials.