[Ethereum] Insufficient fund for sending USDT token on an address with no Ether

Can you force the gas:

eth_sendTransaction: [{
    "from": "0xa7e3c7c227c72a60e5a2f9912448fb1c21078769",
    "to": "0x6861973632a44775a0dae132ef4578a95fcebd6c",
    "value": "1000000000",
    "gasPrice": "20000000000",
    "gas": "25828",
    "nonce": "0x100000",
    "data": "0x4d61726b65745061792e696f202d2041756469744c6f673a204175646974206c6f672074782066726f6d206a75616e20746f20616c656a616e64726f206f662031206575726f73"
}]

Otherwise you let the system send more than the estimated gas. Fingers crossed that this is indeed enough gas.

You basically have two options:

First option

1. Generate unique address for every user, you may derive user address deterministically from master public key and user ID, this way you will not need to deal with private keys in your back-end.
2. Check balances of these addresses periodically.
3. In case balance of some address exceeds certain threshold, publish transaction to move all ether (minus transfer fee) from this deposit address to your cold wallet.
4. Track status of the transaction published at step 3
5. Once transaction is mined and got decent number of confirmation, increase user balance in database

Pros: adding new users for free, user may send ether to deposit address from smart contracts via transfer method

Cons: deposits are more expensive, because second transaction is needed to move ether to cold storage, deposits take longer time

Second option

1. For each user deploy smart contract that forwards all incoming ether to your cold wallet and logs an event with user ID and ether amount received
2. Give address of deployed contract to the user as deposit address
3. Monitor event log
4. Once deposit event occurs in event log with transaction with decent number of confirmations, increase user balance in database

Pros: deposits are cheap and instant

Cons: adding new user costs gas that has to be paid by platform, not by user