NEC SV9300 App ST500

[weatherman1190]

Trying to setup the app ST500 for connecting to SV9300 (SIP extension).
Step by step guide from our PBX-support (I think they are also just guessing).
No success.
Trying to connect to UDP port 5070. Reply from PBX "401 unauthorized" or "503 Service Unavailable".
I've never worked with NEC SV9300 (could not imagine that something like this still exists in 2020)
Anyone ever tried this?
Thanks.

REGISTER sip:10.122.111.10 SIP/2.0
Via: SIP/2.0/UDP 10.122.143.75:5060;rport;branch=z9hG4bKPjJvOvra2s1TWmPQ5Y.VmJk-l16c8S.lyQ
Route: <sip:10.122.111.10:5070;transport=udp;lr>
Max-Forwards: 70
From: <sip:2639@10.122.111.10>;tag=GfDt58LQuOd.HVIrysH.0-w4p7t5Tq71
To: <sip:2639@10.122.111.10>
Call-ID: lp0zpFtnLiXNb96YX.MjSyBb5AnYSXQw
CSeq: 14285 REGISTER
User-Agent: NEC-ST500-IOS/6.1.13601(0186)
Supported: x-nec-roaming
Contact: <sip:2639@10.122.143.75:5060;ob;pn-type=apns:XH7L8MC2V9.com.nec.ios.endd.univerge.st.orca.appstore+a2;pn-prid=12ba2bb3bacab3f4663d2626617c477e9b9f060acdd6db43dc63dfac464f35ad+51c1aacb3854c429123efc796393bbad097ec57108bc2251ce94b4369e528f94;x-nec-profileid=1>
Expires: 3600
Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, INFO, SUBSCRIBE, NOTIFY, REFER, OPTIONS
Content-Length: 0

SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP 10.122.143.75:5060;rport;branch=z9hG4bKPjJvOvra2s1TWmPQ5Y.VmJk-l16c8S.lyQ
From: <sip:2639@10.122.111.10>;tag=GfDt58LQuOd.HVIrysH.0-w4p7t5Tq71
To: <sip:2639@10.122.111.10>;tag=57ed5f7b17990
Call-ID: lp0zpFtnLiXNb96YX.MjSyBb5AnYSXQw
CSeq: 14285 REGISTER

http://WWW-Authenticate:

Digest realm="nec.com", domain="nec.com", nonce="40ff1a235f7b17991", opaque="7e08d905f7b17992", stale=false, algorithm=MD5, qop="auth"
Server: NEC SV9300 / V4.1.6
Content-Length: 0

REGISTER sip:10.122.111.10 SIP/2.0
Via: SIP/2.0/UDP 10.122.143.75:5060;rport;branch=z9hG4bKPj5ksF2Chn7PCgvUyZahPIpyULU7sISU0E
Route: <sip:10.122.111.10:5070;transport=udp;lr>
Max-Forwards: 70
From: <sip:2639@10.122.111.10>;tag=GfDt58LQuOd.HVIrysH.0-w4p7t5Tq71
To: <sip:2639@10.122.111.10>
Call-ID: lp0zpFtnLiXNb96YX.MjSyBb5AnYSXQw
CSeq: 14286 REGISTER
User-Agent: NEC-ST500-IOS/6.1.13601(0186)
Supported: x-nec-roaming
Contact: <sip:2639@10.122.143.75:5060;ob;pn-type=apns:XH7L8MC2V9.com.nec.ios.endd.univerge.st.orca.appstore+a2;pn-prid=12ba2bb3bacab3f4663d2626617c477e9b9f060acdd6db43dc63dfac464f35ad+51c1aacb3854c429123efc796393bbad097ec57108bc2251ce94b4369e528f94;x-nec-profileid=1>
Expires: 3600
Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, INFO, SUBSCRIBE, NOTIFY, REFER, OPTIONS
Authorization: Digest username="2639", realm="nec.com", nonce="40ff1a235f7b17991", uri="sip:10.122.111.10", response="b410d2b5a50eb5f8e78c98c82d6207fc", algorithm=MD5, cnonce="xyz", opaque="7e08d905f7b17992", qop=auth, nc=00000001
Content-Length: 0

SIP/2.0 503 Service Unavailable
Via: SIP/2.0/UDP 10.122.143.75:5060;rport;branch=z9hG4bKPj5ksF2Chn7PCgvUyZahPIpyULU7sISU0E
From: <sip:2639@10.122.111.10>;tag=GfDt58LQuOd.HVIrysH.0-w4p7t5Tq71
To: <sip:2639@10.122.111.10>;tag=31655f7b17993
Call-ID: lp0zpFtnLiXNb96YX.MjSyBb5AnYSXQw
CSeq: 14286 REGISTER
Retry-After: 7
Server: NEC SV9300 / V4.1.6
Content-Length: 0