The global GDP is about $100Trillion. So $300billion is 0.3% per year. It is meant for climate finance and a massive sum, which makes it pretty certain that something ends up in something climate related. Especially with the US likely to leave, which leaves most payers being fossil fuel importers. So they have much less of a reason to promote fossil fuel development. Obviously though a lot of the money will end up in the hands of the rich, thanks to corruption in every country involved.