[osmocom-analog] PBX sends PRACK during call progress which osmo-cc-sip-endpoint rejects

Hey there ! I am excited that this topic started ;-) I am 40 yo guy from Poznan, Poland, about 2 decades ago I had pleasure to work with NMT Centertel Dealer. It brings for me great memories. Recently I managed to collect some NMT phones - at the moment I have more than 10 fully functional NMT phones: Nokia 250, 350, 440, 450, 540, 550, 650, Benefon Delta, Benefon Sigma, Benefon Spica, Motorola Associate 2000. I have four Baofeng radios, buils Linux based pc, bought 2 USB cards and managed to compile, run and work Osmocom - Analog and called phone to phone. Also Computer to phone over headphones. I was also trying to launch LCR, bought ISDN card Fritz, and was attempting to use FritzBox with built - in VOIP - Isdn gate and try to make my NMT phone call PSTN over Voip and mISDN/LCR router. So far no succes. I am not a specialist - self learned electronic - hobbyst. If I could afford it I would buy LimeSDR but for the moment it is a bit expensive for me. Anyway - I have tried OSMO-CC-ENDPOINT as I realised that I will not need any LCR / mISDN / asterisk anymore. I did try many times but all I can get is an update about authentication error with my SIP provider. here is log : osmocom-analog connects to osmo-cc-sip-endpoint, but it looks like SIP-Endpoint does not connects to my SIP provider. I did forward 5060 ports to my linux pc, what could I do wrong: sip.c:1430 debug : Event 29 from SIP stack received (handle=0x55cb861d7980) sip.c: 921 info : Received REGISTER response: 401 Unauthorized (registration) sip.c: 943 debug : Register challenge received sip.c: 178 debug : challenge order received sip.c: 194 notice : No authentication header found sip.c: 954 debug : Register failed, starting register timer sip.c: 956 debug : destroying nua_handle 0x55cb861d7980 (register) using this command line: osmo-cc-sip-endpoint -r mysipnumber@mysipserverip -l localIPosmocom-analog -A SipAccountUser SipAccountPass --remote-auth --register SIPAccountUser@SipServerIp --cc 'screen-called-in "" "myNMTphone"' -P myPublicIP -v 0 Any ideas what do I do wrong? Many greetings for All people in osmocom-analog subjects. I am fascinated about this historical technology. Would be very happy if I could call somebody from my NMT phone ! Regards for all people who work with osmocom-analog subject. Respect to all! Jacek