Blockchain Level
Before a crypto deposit hits Quidax infrastructure, it is processed on the blockchain. Depending on the health of the specific blockchain being used (e.g., Bitcoin, Ethereum, Solana), deposits could be delayed for any of the following reasons:

Mempool Congestion: Think of the blockchain like a busy highway. There is a fixed capacity of data that can fit into each block. When market activity spikes, too many transactions are initiated, and they are forced to wait in a queue called the mempool.
Each transaction must wait its turn to be picked up by a miner or validator and included in a block which could delay a deposit.

Transaction (Gas) Fees: Miners and validators prioritize transactions with higher fees to maximize their profit. Consequently, transactions with higher gas fees are picked first.
If the sending exchange uses a low fee to save costs, the customer’s transaction will be pushed to the back of the queue during periods of mempool congestion, causing significant processing delays on the blockchain.

Confirmation Depth Requirements: One confirmation means your transaction has been included in a block. However, receiving platform exchanges typically require multiple subsequent blocks (confirmations) to ensure the ledger entry is secure and cannot be reversed by an accidental fork. 
For example, Quidax may require 3 confirmations for Bitcoin but only 1 for Solana, depending on the asset's security model. Every additional required confirmation adds several minutes to the final crediting time.

Merchant Action
If a customer confirms that a deposit was successful on the sending exchange, you must first verify the transaction status on the blockchain. If the transaction is still pending on the blockchain, it will not yet reflect in the customer’s wallet. No manual intervention is required at this stage; the customer will be automatically credited once the transaction reaches the required confirmation depth on the blockchain.

Wrong Address/Network 

This is the most common and critical user error. The customer initiated the transaction but sent the funds to an incomplete or wrong address or sent the correct coin (e.g., USDT) over a network not supported on Quidax (e.g., sending USDT via the Avalanche network) or a wrong coin over a network supported on Quidax (e.g., sending BASE over the Ethereum network).

On-chain transactions are cryptographically irreversible. The funds are stuck on the blockchain, and Quidax has no private key control over the destination address/network.
Merchant Action 
Inform the customer immediately that because the funds were sent to an incorrect address/network, Quidax cannot retrieve or reverse the transaction. This is a final resolution.

Compliance Flag

Once a deposit is successfully processed on the blockchain, in line with regulatory requirements, we run an automatic AML filter for each transaction. Transactions are automatically processed into wallet balances, however there is a 1% chance that a transaction may fail the AML flag.

Failing an AML Flag means that the funds may be originating from a high risk wallet or contain traces of risk patterns. Our compliance team manually reviews these deposits and they are cleared in minutes.
Merchant Action 
If a transaction is successful on the blockchain and all deposit protocols were observed (destination tag included, right asset/network sent), escalate immediately to your account manager via your dedicated support channel. Inform the customer their transaction is under standard compliance review and will be processed shortly. A few times, we request for a few additional details to verify the transaction, once that is provided, a deposit is credited almost instantly.

All Protocols Observed, Successful On The Blockchain But Not Credited

This is a rare scenario where the transaction is confirmed on the blockchain, all protocols (like tags) were observed, and no compliance flag was raised, yet the customer has not been credited. This usually points to a temporary third-party system failure.

Merchant Action
Immediately escalate to your account manager, sharing the transaction hash and user ID. Inform the customer that an internal system issue is being addressed by engineers and resolution is the top priority. Issues like this are typically resolved in 2 - 3 working days.

Delayed Deposits Due To Missing Tags (USDt-ton & XRP)

Assets like XRP and USDT on the TON network (USDTTON) require a Destination/Memo Tag to route funds correctly. If the customer forgot to include it, the funds cannot be automatically credited to their wallet. These transactions must go through an intensive, manual tracing process to be identified and credited. Tracing tagless funds through corporate wallets is time-consuming and takes up to 4 to 6 weeks. Once traced, the funds are manually added to the user’s wallet.

Merchant Action 
Share the Transaction Hash and subaccount ID linked to the customer with the Quidax team and manage customer’s expectations regarding the 4 – 6 week resolution timeline.

Please note: Assets that require a destination tag for deposits to be credited usually contain this tag in the webhook payload returned once a wallet address is called or generated.