Answer
Custom web services are built as BizAPI customizations through IFS Connect, developed as part of Middle Tier Integration development — this is genuine customization work, not a configuration-only task. Separately from building your own, IFS already ships a large set of out-of-the-box web services bundled with the application, which can be browsed directly via the Interface Browser rather than needing to be built from scratch. Whether a developer license is specifically required for building new custom BizAPIs depends on your particular licensing agreement, so that's a question for your IFS account representative or partner rather than something with one universal answer.