It's so hard to find relevant information on anything since people want you to buy the official parts and controllers, not make your own, so they withhold information or outright lie sometimes...
Huh? The soft-starter info is all over the web. The manufacturer and distributors have it posted. The links in the product document work for me. Here is a direct link to the instruction sheet on the ABB server:
The ST (start) input requires a maintained +24 vdc level to run the motor. The soft-start also requires overcurrent protection in the form of fuses or a manual motor starter (MS325) with integrated magnetic breaker.