There are 3 forms of Power BI-
Power BI Desktop (PBID)- This is free for all and is used to build reports.
Power BI Services (PBIS)- This is a SaaS application. It is used to create reports and share them. This app is accessed on the web through powerbi.com. The reports are stored in logical containers called workspaces. You can publish your Desktop reports here into workspace and embed reports from here.
Power BI Embedded (PBIE)- this is a PaaS application which enables you to embed reports into your app. It can be used to implement auth and show only specific reports to particular users. All users in your app can see all the different content and reports, based on your app logic, because you manage access to report via PBIE SDK.
So, when your consumers utilize PBIS, they're using the Microsoft Web App; if you want to include the same reports in your app, use PBIE and the SDKs provided.
In terms of licenses, In reality, there is just one type of license: PRO. If your users want to utilize PBIS to publish and distribute reports, they must all have PRO licenses. Therefore, unless you choose to share your reports and analysis, you can use any of the tools for free. You must pay if you need to share.
While in PBIE, you create your app and manage your users as you see fit. PRO licenses should not be granted to them. Only one license is required to save your reports. This is referred to as a service account. This is an ordinary PBIS user who has purchased a PRO license. You may use it to publish reports and save them in PBIS, while your app uses it to load and embed reports. If you have 1000 users, you can purchase one license and use it to publish your work, and all users will be verified and authorized in your app. Also, once you're in production, you'll need to purchase capacity - Power BI Embedded Services at Azure. The price is determined by the renderings.