Fund a testnet account

Most users don’t need this. In the Arcus testnet web app, connect your wallet and click Testnet Deposit to instantly credit ~$1,000 in USDG of paper-trading collateral — that’s enough for nearly everything. This guide is for API traders who need a larger balance, or who want to fund programmatically as part of a test harness.

The flow

Funding is an on-chain deposit on Robinhood Chain testnet. The exchange credits your trading account automatically once it observes the deposit on-chain (typically under a minute). The steps never change:

Mint the collateral token

The testnet collateral token (USDG) has an open mint — anyone can mint themselves test tokens. Mint the amount you want to deposit.

Approve the deposit proxy

Approve the deposit proxy contract to pull your USDG. The spender is the deposit proxy, not the bridge.

Call `initiateDeposit`

Call initiateDeposit on the deposit proxy. It pulls your USDG, wraps it into the margin token, and forwards it to the bridge. owner must equal the wallet that signs the transaction.

Wait for the credit

Poll GET /v1/account until your balance reflects the deposit. It also shows up as an APPLIED DEPOSIT on GET /v1/accountTransferUpdates.

That sequence — mint → approve → initiateDeposit → wait — is stable. The contract addresses below are not.

Testnet parameters

These addresses are testnet deployment details that change on every redeploy or network reset — confirm them before relying on them in automation. A stale address fails in one of two ways: an obvious WrongToken / transfer revert, or a transaction that succeeds on-chain but never credits your account (you minted/approved/deposited against a retired deployment that the live exchange no longer watches). The flow is stable; the values are not.

You only ever interact with two contracts: the collateral token (USDG) and the deposit proxy. The proxy forwards to the bridge internally, so you never call the BridgeVault directly.

Parameter	Value (testnet, verify before use)
Chain ID	`46630`
RPC URL	`https://rpc.testnet.chain.robinhood.com`
`USDG` — collateral token (`MockERC20`, 6 decimals, open mint)	`0x293b337712d4312776a3a2d292f44410e7873bad`
`PaxosDepositProxy` — deposit entry point	`0xb872366eef371d4afb7c6d4d2abd53c17292a34d`

Amounts use the token’s 6 decimals — e.g. $1,000 = 1000000000, $100,000 = 100000000000. Your wallet also needs a small amount of RH-testnet ETH (≈0.001) to pay gas for the transactions below. There is currently no public faucet for RH-testnet ETH — seed a fresh wallet by transferring from a wallet you already gas-funded, or ask the Arcus team. (When seeding wallet-to-wallet, note the chain rejects a bare 21,000-gas transfer with intrinsic gas too low — let your tooling estimate gas rather than hard-coding the classic minimum.)

Deposit with `cast`

Using Foundry’s cast. $KEY / $ADDR are the depositing wallet’s private key / address:

RPC=https://rpc.testnet.chain.robinhood.com
USDG=0x293b337712d4312776a3a2d292f44410e7873bad
PROXY=0xb872366eef371d4afb7c6d4d2abd53c17292a34d
AMT=1000000000   # $1,000 at 6 decimals

# 0. Sanity-check the chain and that you have gas
cast chain-id --rpc-url $RPC          # → 46630
cast balance $ADDR --rpc-url $RPC     # → must be > 0 (RH-testnet ETH for gas)

# 1. Mint test USDG to your wallet (open mint, testnet only)
cast send $USDG "mint(address,uint256)" $ADDR $AMT --rpc-url $RPC --private-key $KEY
# 2. Approve the deposit proxy to pull your USDG (spender is the PROXY, not the bridge)
cast send $USDG "approve(address,uint256)" $PROXY $AMT --rpc-url $RPC --private-key $KEY
# 3. Deposit into account index 0 — owner must equal the caller, token must be USDG
cast send $PROXY "initiateDeposit(address,uint16,address,uint256)" $ADDR 0 $USDG $AMT --rpc-url $RPC --private-key $KEY

The initiateDeposit arguments are (owner, accountIndex, token, amount). Use accountIndex 0 unless you trade a non-default subaccount, and token must be the USDG address (the proxy rejects anything else with WrongToken).

Deposit programmatically (web3.py)

The same three transactions from a test harness, using web3.py and the wallet’s private key:

from web3 import Web3

RPC   = "https://rpc.testnet.chain.robinhood.com"
USDG  = Web3.to_checksum_address("0x293b337712d4312776a3a2d292f44410e7873bad")
PROXY = Web3.to_checksum_address("0xb872366eef371d4afb7c6d4d2abd53c17292a34d")
AMT   = 1_000_000_000  # $1,000 at 6 decimals

w3 = Web3(Web3.HTTPProvider(RPC))
assert w3.eth.chain_id == 46630
acct = w3.eth.account.from_key(PRIVATE_KEY)
assert w3.eth.get_balance(acct.address) > 0  # RH-testnet ETH for gas

usdg = w3.eth.contract(address=USDG, abi=[
    {"name": "mint",    "type": "function", "inputs": [{"name": "to", "type": "address"}, {"name": "amount", "type": "uint256"}], "outputs": []},
    {"name": "approve", "type": "function", "inputs": [{"name": "spender", "type": "address"}, {"name": "amount", "type": "uint256"}], "outputs": [{"type": "bool"}]},
])
proxy = w3.eth.contract(address=PROXY, abi=[
    {"name": "initiateDeposit", "type": "function", "inputs": [
        {"name": "owner", "type": "address"}, {"name": "accountIndex", "type": "uint16"},
        {"name": "token", "type": "address"}, {"name": "amount", "type": "uint256"}], "outputs": []},
])

def send(fn):
    tx = fn.build_transaction({"from": acct.address, "nonce": w3.eth.get_transaction_count(acct.address)})
    signed = acct.sign_transaction(tx)
    receipt = w3.eth.wait_for_transaction_receipt(w3.eth.send_raw_transaction(signed.raw_transaction))
    assert receipt.status == 1, f"reverted: {receipt.transactionHash.hex()}"
    return receipt

send(usdg.functions.mint(acct.address, AMT))                          # 1. mint
send(usdg.functions.approve(PROXY, AMT))                              # 2. approve the proxy
send(proxy.functions.initiateDeposit(acct.address, 0, USDG, AMT))     # 3. deposit

Verify

# Balance should reflect the deposit
curl "https://api.testnet.arcus.xyz/v1/account?address=$ADDR&accountIndex=0"

# The deposit shows up here as an APPLIED DEPOSIT
curl "https://api.testnet.arcus.xyz/v1/accountTransferUpdates?address=$ADDR&limit=50"

An address with no activity at all returns 404 ("this account has no activity yet") from GET /v1/account — that’s the expected empty state, not an error. Registering an API key already counts as activity: an onboarded-but-unfunded account returns 200 with equity: "0". Once the deposit applies, the response reflects the credited balance.

Troubleshooting

Symptom	Cause / fix
`initiateDeposit` reverts with `WrongToken`	The `token` argument must be the `USDG` address. If it already is, the configured underlying may have changed — confirm the current addresses.
Reverts on transfer / allowance	The approval (step 2) must be on `USDG` with the `PaxosDepositProxy` as spender — not the bridge. Re-run step 2.
`intrinsic gas too low` / `max fee per gas less than base fee`	Top up the wallet’s RH-testnet ETH and retry; the base fee can rise between blocks. This also fires on a hard-coded 21,000-gas ETH transfer — let your tooling estimate gas.
`initiateDeposit` reverts once, with mint and approve confirmed	Transient — retry the identical transaction before debugging. Verify the allowance is in place first (`allowance(owner, PROXY)` ≥ amount); a straight re-send has been observed to succeed.
Transaction succeeds but no credit appears	Confirm the deposit tx landed on-chain. If it did and the balance still hasn’t moved after a few minutes, the exchange’s deposit observer didn’t pick it up — this can be per-deposit or a temporary outage of the crediting pipeline itself (more likely shortly after a testnet reset). Flag it to the Arcus team with your wallet address and the tx hash; the deposit credits once the observer catches up.

Next steps

With a funded account, place your first order — Trade over REST or Trade over WebSocket.

API trading

MCP integration

Fund a testnet account

The flow

Testnet parameters

Deposit with `cast`

Deposit programmatically (web3.py)

Verify

Troubleshooting

Next steps

​The flow

​Testnet parameters

​Deposit with cast

​Deposit programmatically (web3.py)

​Verify

​Troubleshooting

​Next steps

The flow

Testnet parameters

Deposit with `cast`

Deposit programmatically (web3.py)

Verify

Troubleshooting

Next steps