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Most users don’t need this. In the Arcus testnet web app, connect your wallet and click Testnet Deposit to instantly credit ~$1,000 USDC 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.

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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:
1

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.
2

Approve the deposit proxy

Approve the deposit proxy contract to pull your USDG. The spender is the deposit proxy, not the bridge.
3

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.
4

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.

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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.
ParameterValue (testnet, verify before use)
Chain ID46630
RPC URLhttps://rpc.testnet.chain.robinhood.com
USDG — collateral token (MockERC20, 6 decimals, open mint)0x022f49dbd588908b5a1805886c2107f0315223b4
PaxosDepositProxy — deposit entry point0x10096bec721173f70add303affc235d7c99fbfd4
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 cast send transactions below.

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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=0x022f49dbd588908b5a1805886c2107f0315223b4
PROXY=0x10096bec721173f70add303affc235d7c99fbfd4
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).

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Verify

# Balance should reflect the deposit (testnet accounts may carry a seed balance — check the delta)
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"
Testnet accounts may already show a small seed balance, so assert the delta (balance after − balance before), not the absolute value.

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Troubleshooting

SymptomCause / fix
initiateDeposit reverts with WrongTokenThe token argument must be the USDG address. If it already is, the configured underlying may have changed — confirm the current addresses.
Reverts on transfer / allowanceThe 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 feeTop up the wallet’s RH-testnet ETH and retry; the base fee can rise between blocks.
Transaction succeeds but no credit appearsConfirm the deposit tx landed on-chain. If it did and the balance still hasn’t moved after a minute, the deposit wasn’t observed — flag it to the Arcus team with your wallet address.

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Next steps

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