Unable to run BLE GATT service on Nordic Thingy 52

I can't get Thingy to provide a GATT service. After reading everything I could find online, I still have no idea what I could be doing wrong.

Advertising work fine, I can see the 0x180D service in the advertisement (I'm using NRFconnect on iOS to check, but have the same effect with other tools as well).

But when I connect only the standard UART RX and TX services are visible. Nothing else.

The code below is taken from another stream and appeared to work on a Ruuvitag. (I've tried various versions, but without any change in effect).

NRF.setServices({
  0x180D: { // heart_rate
    0x2A6E: { // heart_rate_measurement
      notify: true,
      readable: true,
      value : [0]
    }
  }
}, { advertise: [0x180D], uart: false });


var cnt = 0;

setWatch(function() {
  if(cnt++ % 2 === 0)
    LED1.set();
  else
    LED1.reset();
  NRF.updateServices({
    0x180D : {
      0x2A6E : {
        value : [cnt],
        notify: true
      }
    }
  });
}, BTN, { repeat:true, edge:"rising", debounce: 50 });

The LED toggles just fine, so obviously the function gets called.

And, yes, I do disconnect the Web Bluetooth IDE from Thingy before I check the services.

Any help would be much appreciated!
Thanks,

Bernd