The multi_token parameter it's only available for TRC-20, BEP-20 and ERC-20 networks. It's also an optional parameter, meaning that you don't need to set it while making a request. It's default value is 0.
This parameter allows the same same address_in to receive payments in any token supported by our system.
When setting this parameter you should make sure your wallet address (address_out) supports the tokens you expect your clients to pay with. CryptAPI cannot reverse any transaction any payment of a token unsupported by your wallet.
This parameter also means your clients can pay on any token supported by our system, even tokens with very different prices, so your system should check the coin field and make the appropriate price conversions. If you wish to receive 1000 USDT (or equivalent) and your client sends 1000 DOGE, your system should be able to handle that scenario.