Thanks for your answers guys, that’s really helpfull.
Something I didn’t get befort and that I just understood now : RTCM3 protocol is used to transfer corrections from the base station to the rover through NTRIP (server (Rpi/Arduino/ESPrtk) / caster (rtk2go servers) / client (AOG)). Then, NMEA protocol is used to send back corrected position using GGA messages from the rover to AOG through serial. In fact, BOTH RTCM3 and NMEA are used in the whole system, while I thought there was a “good” protocol to choose and a “bad” one to avoid. I leave this explanation here for people as lost as i am (or was).
Anyway, now RTK2GO displays precisely the coordinated I computed, so that’s satisfying. @pniels my interface did look quite different than yours though :
I think I will go with the same messages as you. According to @Alan.Webb, you use MSM7 messages, which are more accurate, so I’ll go with them.
I also use refresh rates of 1 Hz for MSM7 messages, and 0.1 Hz for 1005 message, as recommended. Toriem detailed in another thread how to set messages rates in U-center (What RTCM3.x messages are people using? - #2 by torriem)
Again, thank you verry much for your help