Did anyone manage to get SBAS reliable working on B2?

I have tried it with PCAS02, the command to change the update rate and without the $ included in the checksum it changes nothing while including it works.

print(require("pcas").checksum("$GPGLL,5300.97914,N,00259.98174,E,125926,A")); creates a checksum of 28 which matches your example. Doing the same without $ calculates 6F as checksum.

require("pcas").checksum is as follows:

function checksum(cmd) {
  var cs = 0;
  for (var i = 1; i < cmd.length; i++)
    cs = cs ^ cmd.charCodeAt(i);
  return cmd + "*" + cs.toString(16).toUpperCase().padStart(2, '0');
}