device tree overlay for heartbeat not working - overlay

Question

First of all, hello!
I wrote a device tree overlay for heartbeat function on a gpio (you can see the dts file below).
It is loadad successfully, and I could see the trigger file in userspace:
root#beaglebone:~# cat /sys/devices/platform/bone_capemgr/slots
0: PF---- -1
1: PF---- -1
2: PF---- -1
3: PF---- -1
4: P-O-L- 0 Override Board Name,00A0,Override Manuf,cape-univ-emmc
6: P-O-L- 1 Override Board Name,00A0,Override Manuf,issd-heartbeat
root#beaglebone:~# cat /sys/class/leds/beaglebone\:yellow\:usr0/trigger
none nand-disk usb-gadget usb-host mmc0 mmc1 timer oneshot [heartbeat] backlight gpio default-on
Everything looks ok but I cannot see heartbeat on the pin.
I verified the led is working, I can pull it low and high with no problem when it's configured as output gpio.
I don't know where to look now, so if anyone can direct me, it's enough. Thanks.
DTS file:
/dts-v1/;
/plugin/;
/ {
compatible = "ti,beaglebone", "ti,beaglebone-black";
/* identification */
part-number = "issd-heartbeat";
version = "00A0";
/* state the resources this cape uses */
exclusive-use =
/* the pin header uses */
"P8.8", /* heart beat LED*/
/* the hardware ip uses */
"gpio2_3";
fragment#0 {
target = <&am33xx_pinmux>;
__overlay__ {
indicator_pins: indicator_pins {
pinctrl-single,pins = <
0x094 0x07
>;
};
};
};
fragment#14 {
target = <&ocp>;
__overlay__ {
indicator_pins {
compatible = "gpio-leds";
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <&indicator_pins>;
led0 {
label = "beaglebone:yellow:usr0";
gpios = <&gpio3 3 0x00>; /* gpio3 is gpio2*/
linux,default-trigger = "heartbeat";
default-state = "off";
};
};
};
};
};