My ad is not eligible for impressions, my listing is not in the buy box

I recently add my products and start selling on Amazon. To sell my own brand I’m trying to register my brand but it looks it is not available now and try to make ad on my listings to able to sell them but I’m receiving this “Your ad is not eligible for impressions because your listing is not in the buy box.” So is there any way to make my listing in the buy box or do I need to wait for a long time? And is it possible to make some other ads on Amazon by avoiding these buy box, registered brand or fulfilled by amazon restrictions?

Time.
You have to qualify for the buy box - 90 days is the figure bandied about though it is believed FBA can bypass that requirement.

No idea about other ads on amazon.
You can always advertise off amazon.