Azure Data Factory - help needed to ingest data, that uses an API, into a SQL Server instance

Postman is only a test client; its collection is useful because it shows the exact token endpoint, request body, headers, API path and pagination. ADF does not need Postman at runtime.

If iLevel uses standard OAuth 2 client credentials, create a REST linked service and set Authentication to OAuth2 Client Credential. Supply the token endpoint, client ID, client secret, and the scope or resource exactly as iLevel specifies. Keep the secret in Key Vault. Then use Copy activity with REST as the source and Azure SQL as the sink; put the selected API path in the relative URL and configure pagination and mapping for the returned JSON.

A successful linked-service test may confirm only that the host is reachable, so adding “xxx” does not prove the resource exists.

If iLevel's token flow is nonstandard, use a Web activity POST with Content-Type application/x-www-form-urlencoded, then pass Bearer plus the returned access token to Copy activity. Enable secure input and output so the secret and token are not exposed in monitoring.