Hi Dmitry,
When you upload a artifact to RQM using REST API,

1. Either you provide an externalID at the end or url and PUT resource. You already have id :)
   An example of testscript URL with externalID provided
   https://localhost:9443/jazz/service/com.ibm.rqm.integration.service.IIntegrationService/resources/Quality+Manager/testscript/myexternalID
   
2. If externalID not provided, you can POST it, then RQM might auto generate a id for you e.g. slug__GCglELu-EeGBn97XJrT_5Q. In this case you should look for the response header Content-Location , it's value you should use to link other artifact.
   An example of testscript URL without externalID provided
   https://localhost:9443/jazz/service/com.ibm.rqm.integration.service.IIntegrationService/resources/Quality+Manager/testscript
   And support you received something slug__GCglELu-EeGBn97XJrT_5Q in content location then url will become https://localhost:9443/jazz/service/com.ibm.rqm.integration.service.IIntegrationService/resources/Quality+Manager/testscript/slug__GCglELu-EeGBn97XJrT_5Q
   
   

ExternalID is an optional unique id given to a artifact where two artifact of same type (say Test Case) can not have same externalID.
An alternative to generate url without using externalID is this way
https://localhost:9443/jazz/service/com.ibm.rqm.integration.service.IIntegrationService/resources/Quality+Manager/testscript/urn:com.ibm.rqm:testscript:4

Here testscript is type of resource and 4 is the internal integer id.

Hope it helps