Adobe target server-side for A/B testing in APP

Hi We are setting up an A/B testing to serve different JSON in an APP.

For architectural reason we need to use Adobe Target (server side) We did some testing, everything seems to work, except Adobe Analytics tracking.

I've read some articles and community post, almost all point to the following article

https://experienceleague.adobe.com/en/docs/id-service/using/implementation/ecid-a4t-target

But it refers to a scenario with bowser as client. What if we have an APP as the client? How do I retrieve the SDID that seems essential for target analytics stitching?

Regards

Giuseppe