You pay with the native coin of the chain the token lives on: BNB on BNB Chain, SOL on Solana and ETH on Robinhood Chain. Each coin lives on one chain, so a Solana coin cannot be bought from a BNB wallet.
On Solana the creator can choose another token to pair with, such as USDC from an approved list. For those coins the panel shows which token it asks for. Always read the panel and the wallet request before you confirm.
Keep a little of the chain's native coin in the wallet for the network fee, whatever you buy with.