In the UK, credit card issuers are legally liable if you use the card to buy an item or service from a supplier registered with the card company. So if e.g. the supplier goes bust and you don’t receive what you ordered, the card issuer is liable to re-fund you if the transaction was between £100 and £30,000.
The reasoning is that the card issuer went into a profitable arrangement with the supplier before the consumer eve got involved, so they have a responsibility for the suppliers they allow to accept payments using their cards.
I can’t right now confirm if this applies also to cash deposits made to a broker through a card but the way I read the blurb I believe it does.
Maybe its the same in other jurisdictions?