The majority of roadmaps look better on paper than in reality. The cause is that the idea of an IoT project should be thoroughly evaluated for its feasibility. It’s not advisable to underrate the discovery phase of your project as it may appear many things require even deeper clarification and investigation.
Work hard on the discovery stage with your software vendor: they will gather and analyze your requirements to create an app for IoT, conduct deep research and identify a project scope that will result in a more detailed roadmap and an accurate estimate that excludes excess payment.