Invalid lock refid NMEA

Hello

I have GPS antenna to ublox module connected to raspberry pi GPIO. I went with this setup because the usb GPS antenna I was using before does not provide PPS (pulse per second) which is needed to provide time to a network. I'm using Chrony because it interpets PPS better than NTP. I'm paraphrasing and over simplifying mainly because I don't understand much of the ins and outs of how it all works.

When I check the status of chrony I get the following

chrony.service - chrony, an NTP client/server
Loaded: loaded (/lib/systemd/system/chrony.service; enabled; preset: enabled>
Active: active (running) since Sat 2024-06-29 11:15:06 PDT; 1 week 3 days >
Docs: man:chronyd(8)
man:chronyc(1)
man:chrony.conf(5)
Process: 795 ExecStart=/usr/sbin/chronyd $DAEMON_OPTS (code=exited, status=>
Main PID: 825 (chronyd)
Tasks: 2 (limit: 8731)
CPU: 56.429s
CGroup: /system.slice/chrony.service
825 /usr/sbin/chronyd -F 1
832 /usr/sbin/chronyd -F 1

Jun 29 11:15:06 time systemd[1]: Starting chrony.service - chrony, an NTP clien>
Jun 29 11:15:06 time chronyd[825]: chronyd version 4.3 starting (+CMDMON +NTP +>
Jun 29 11:15:06 time chronyd[825]: Frequency 12.842 +/- 0.104 ppm read from /va>
Jun 29 11:15:06 time chronyd[825]: Using right/UTC timezone to obtain leap seco>
Jun 29 11:15:06 time chronyd[825]: Loaded seccomp filter (level 1)
Jun 29 11:15:06 time systemd[1]: Started chrony.service - chrony, an NTP client>
Jun 29 11:15:06 time chronyd[825]: Invalid lock refid NMEA

Everything looks good (to me) except the last line. When I look at chrony.conf I think the following should be taken out

# Use Debian vendor zone.
pool 2.debian.pool.ntp.org iburst

and add the following;

#GPS serial data reference (NTP0)
server 127.127.28.0
fudge 127.127.28.0 refid GPS

# GPS PPS reference (NTP1)
server 127.127.28.1 prefer
fudge 127.127.28.1 refid PPS

Is there something else I'm missing? Also I've been assured that NMEA software is not needed to make use of the PPS

thank you for any help