fcm notification not working 'give me message browser not support'

Excuse me, support team. I'm asking if Median.co allows Firebase FCM for notifications, as I've set it up on my website, but it's not working in the app I converted. If it is supported, could you please assist me in getting it to work? If it's not supported, what alternatives would you recommend so I can communicate with my clients through Firebase push notifications? If there’s no solution, I would like to cancel my Median account and discontinue its use.