PowerBI API: license clarification

[erossini]

I’m creating some website with integrate PowerBI. The integration is via PowerBI API based on my license PowerBI Pro.

The websites provide the security layer and each customer can see a different PowerBI report. Based on the Microsoft documentation and this port on PowerBI community (Solved: PowerBI REST API License/Azure - Help - Microsoft Power BI Community) we have to pay only the license for a PowerBI Pro and consuming the reports via PowerBI API is unlimited free.

I googled a bit and I found this other link 

https://community.powerbi.com/t5/Service/Power-BI-Embedded-REST-API-cost-architecture/td-p/290177

I don't understand what the real licence policy is. Could you clarify what the company has to pay?