Choice is based on the fact - if you Xojo APP going to have LOCAL DB or Client-Server db. Both also is possible.
1) LOCAL DB
- you need Valentina DB ADK. 199$ for single OS, 399$ for 3 OS
Read More on site: https://valentina-db.com/en/valentina-database-adk-overview
Most probably you need our VDN - Valentina Developer Network product, which includes Valentina Embedded Server.
This product allows you to deploy OEM VServer royalty free. Exists few level of price depending on the connection number.
Price starts with $599
Read More on site: https://valentina-db.com/en/valentina-developer-network-overview
3) with Valentina DB ADK, it is possible develop hybrid Apps, which can work in the same time with a LOCAL VDB and Remote Valentina Servers.
4) with Valentina Embedded Server you get in hands not only Valentina DB Server, but also Report Server, SQLite Server, Forms Server. They all are built-into VSERVER.