I am guessing that the prf is the authentication algorithm which you would configure when you create the proposal using sha-1
What is the prf? can you give a full description of it and we may be able to find the Juniper equivalent. Pardon my ignorance of Cisco.
Does your version of JunosOS support IKEv2?
Did you configure Juniper to use Ikev2? This is the onoly thing I can see so far as to why it is not working. If we could see even the details of the debug logs, we may find something else.
set security ipsec proposal <ipsec_proposal> authentication-algorithm sha1
set security ike gateway <gateway> version v2-only
What is the prf? It seems to be Pseudo random function, which equates to the hashing algorithm used for authentication, which you have configured. Maybe try a different algorithm? Can you give a full description of it and we may be able to find the Juniper equivalent. Pardon my ignorance of Cisco. I searched for an explanation but could not find one other than , just a configuration using the term.