Do not use anything to fill it. Best thing to do is nothing. Just keep it open and airy, trim any other plants away from it. And make sure a sprinkler isn't hitting it in that spot. Also, no deep or excessive mulch around this palm.

Palms are not true trees so it will never heal that hole. The hole is an open passage for any potential pathogens. But I have seen palms with holes that have been alive for decades.

Thank you very much for that Eric. In fact, there is a sprinkler head just feet away from the site and there is a light layer of mulch inches away from the base.

I'll be changing the sprinkler head to reduce the impact of watering on that area.

Thanks again.