I would suggest you using DI Server instead of DI API as DI API is more recommended for .NET platform however you are using PHP so it may run into compatibility issue.
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Note that DI Server (Data Interface Server) is a Component Object Model service running on a server which allow multiple clients to read and write SAP B1 database using SOAP messages.
SAP B1 DI Server allows you to develop SOAP based solutions that can be used to read, write, update, and remove data objects.
Below are the key differences about use of DI Server and DI API:
For more details about use of SAP B1 DI server, you can refer this link: