@Matas Kaucikas , I am assuming you are trying to insert modelID as one of the instance field of an instance in TSI through our ingestion service.
If that is the case, unfortunately we cant insert instance fields through our ingestor service. Instead you can call our API to insert instance field and its values. The API could be called from your "ProcessDTUpdatetoTSI" function or using upload JSON option in TSI model page.
In either case, you cant upload the DTDL model directly as you are trying in the screenshot provided by you. TSI has its own syntax please refer to the attachment for details
43986-sample-model.txt
Please refer to the following documentation for information about TSI model, Patch Syntax and API details!
https://learn.microsoft.com/en-us/azure/time-series-insights/concepts-model-overview
https://learn.microsoft.com/en-us/rest/api/time-series-insights/dataaccessgen2/timeseriesinstances/executebatch#instancesbatchput
Please let me know if I could be of further help!