Coins of the Ethereum family have three main parameters in the advanced settings menu when sending: Gas Limit, Nonce and input data. This article will explain what these are, but you should not need to change any of these values in everyday use.
Nonce
The nonce value of a transaction is the sequence number of transactions sent from your account, starting from 0. This means that the first transaction confirmed from an address will always have nonce 0. The next will always have nonce 1, then 2 and so on. Nonces must confirm in order, without skipping. Coinomi automatically increments the nonce after sending, effectively placing new transactions at the end of the queue without affecting other pending transactions.
Setting a value too low
If you try to send a new transaction with a nonce that has already confirmed, the new transaction will be invalid. Trying to send it in this case will simply return an error saying the nonce is too low.
Setting a value too high
If you make a transaction with a nonce too high, it will be valid, but will not immediately confirm. It will be held by validators until all lower nonces have confirmed. It will remain pending until you have enough ETH balance and fees paid are high enough, at which point it will immediately confirm. Transactions have no "expiration date" and can be held indefinitely.
Setting the same value as an unconfirmed transaction
If you have an unconfirmed transaction, making a new one with the same nonce and higher fee will essentially replace the unconfirmed one. Everything about the new transaction will take precedence, including value and destination address. You can in essence cancel an unconfirmed transaction by replacing it with one sending 0 ETH to your own address. The only net difference in your balance will be the deducted transaction fees which must always be paid to the network. You can read specific instructions about replacing a pending transaction here.
Gas Limit
This option limits the amount of gas that can be used in the transaction. Think of it as limiting the operations and computation the transaction can perform. If you don't know what value to use, we recommend leaving it the way it is. It will be automatically calculated by Coinomi and use an adequate value for most cases.
Setting a limit too low
If the transaction ends up needing more gas than the set limit, the transaction will confirm on the blockchain with a failed state, because it couldn't complete all operations. The transaction will have no effect except for the payment of the transaction fee according to the gas limit.
Setting a limit too high
There is no major downside of setting a high gas limit. When the transaction confirms, you will only pay fees for the gas that was actually used. The main drawback is needing to keep a higher ETH balance in reserve for the possibility of the full limit being used.
A basic ETH transfer from one address to another uses 21,000 gas. A token transfer, smart contract or defi operation can use from 50,000 to 200,000 gas. More complex transactions like NFT minting can use more.
Input data
This field is for entering specific data required in some transactions. For most users this will never be used manually as transactions which require such data automatically fill this, For example Dapp/DEX transactions.