The purpose of this study is to address uncertainty for the implementation of functionality concerning invoice management in the context of the customer relationship management (CRM) system Salesforce by providing design guidelines. It is a qualitative research project that follows a user-centered design (UCD) approach. Seven themes covering perceived difficulties were identified from a diverse set of stakeholders. The themes were analysed in a workshop where two Salesforce developers used their expert judgment to address the themes with liable design suggestions. This was followed by a heuristic evaluation session where an external Salesforce developer evaluated compressed versions of the design suggestions, leading to a concluding proposal of guidelines: 1) Comprehensive error handling and feedback, 2) Modular architecture, 3) Clarify systems relationship and provide detailed information, 4) Group similar functionality according to user role and provide direct feedback, 5) Understand user needs and utilize data graphics 6) Provide transparency for errors when possible, and 7) Provide traceable documentation based on functionality and workflows.