Hi @Vishesh Taneja
Welcome to the Microsoft Q&A platform, and thank you for posting your query.
The Microsoft Information Protection SDK does not incur any metered API costs. The SDK is a free tool that allows you to develop applications that use sensitivity labels to protect your data. You can use the SDK to apply sensitivity labels to documents as part of a migration from On-Prem to SharePoint Online without incurring any additional costs.
However, please note that there may be other costs associated with using Microsoft services such as Azure or SharePoint Online. These costs may include storage costs, data transfer costs, and other usage-based costs. You should review the pricing and licensing information for these services to understand the costs associated with using them.
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