RAK7243 pilot pro gateway [WARNING]: [gps] could not get a valid message from GPS (no time)

I own a RAK7243 pilot pro gateway without LTE.
i am using latest firmware downloaded by here https://downloads.rakwireless.com/LoRa/Pilot-Gateway-Pro-RAK7243/Firmware/RAK7243_Latest_Firmware.zip.
I would like to set up the gateway to send beacons to test class B functionalities.
However, i always get spammed with this message
[WARNING]: [gps] could not get a valid message from GPS (no time)
And i see no beacons being sent.
If i log into the chirpstack installed in the gateway, i can see that the position of the gateway is correctly acquired. Still, seems that it cannot get the gps time.
The antenna is placed outdoors and seems sufficiently open to acquire signal from gps satellites.
Seems that gps is connected over serial port “gps_tty_path”: “/dev/ttyAMA0”

How can i enable beacon sending and get rid of this message?

Thank you very much,

Best Regards

Do you have access to this information?

Sometimes, yes,
valid reference
Sometimes, no, I get “invalid time referenc, XX sec” where xx is a different value everytime, i guess is too old.
Beacons should be sent automatically if gps time is synchronized?

The current protocol used by the gateway is version lorawan 1.0.2, which means that classB mode is not supported yet, and if you want to use it, you will need to modify the configuration file to accommodate the lorawan 1.0.3 protocol.

Could you please provide me your email address? And tell me which band you want to use for the test, and I will provide you with the configuration file.

i tried adding the following lines
but with no success.

It needs to modify something else, not just a little bit here.