Send USDC in sandbox

Send test USDC from one sandbox wallet to another on the same network, and know which crypto sends sandbox cannot settle today.

Use this recipe to send test USDC from one sandbox wallet to another on the same network, and to find out which crypto sends sandbox cannot settle today.

Who it is for. A crypto payroll tool that pays contractors in USDC and wants to test sends between its customers' wallets.

Status. Available for a same-network send. Not yet available in sandbox for a cross-network send, or for a failed send on purpose.

Money example

Your customer's sandbox Polygon wallet holds 200 test USDC.
You send 75.00 USDC to another sandbox Polygon wallet.
The send completes in about 3 seconds. The source wallet then shows 125, and the destination wallet shows 75.

Before you start

A sandbox wallet that holds test USDC. Read its balance with GET /v1/wallets/{wallet_id}. On EVM networks this balance is the sandbox test dollar. USDC from a public faucet does not show in it. Putting test dollars on a standalone EVM wallet through the API is Not yet available. Ask support if you need a funded sandbox wallet.
A destination address on the same network.

Find out what is required

The network, asset and memo rules of the destination network are the same as in live. See Send stablecoins to an outside wallet.

Steps

1. Send

Send a normal POST /v1/transfer with the crypto destination, exactly as in Send stablecoins to an outside wallet, with your sandbox key. Do not add _simulate_web3.

2. Follow it

curl --request GET \
 --url https://api.gravv.xyz/v1/transactions/1a2a73ed-562b-4f79-8374-59eef50bea63 \
 --header 'Api-Key: <API_KEY>'

const response = await fetch("https://api.gravv.xyz/v1/transactions/1a2a73ed-562b-4f79-8374-59eef50bea63", {
method: "GET",
headers: {
"Api-Key": process.env.GRAVV_API_KEY,
},
});
console.log(response.status, await response.json());

import os

import requests

response = requests.get(
"https://api.gravv.xyz/v1/transactions/1a2a73ed-562b-4f79-8374-59eef50bea63",
headers={
    "Api-Key": os.environ["GRAVV_API_KEY"],
},
)
print(response.status_code, response.json())

A same-network send settles in seconds. You receive transfer.status.pending events that carry a tx_hash, then transfer.status.completed. For a USDC wallet source, the transfer response shows amount_currency USD.

3. Read the balances

Call GET /v1/wallets/{wallet_id} for both wallets. A wallet can show "stale": true for a few minutes after a send. If it does, read it again later.

What can go wrong

Response	Why	Fix
The send never completes	You added `"_simulate_web3": "success"`	Remove it and send a normal transfer
`pending` with no event at all, and the wallet is not debited	You added `"_simulate_web3": "failed"`	Remove it
For a cross-network send, Gravv sends `transfer.status.failed` while the row stays `pending`, or the send stays `pending`	Cross-network sends do not settle in sandbox today	Test same-network sends only
400 `insufficient balance` from a Stellar or Solana wallet	The wallet holds no test dollars	Send from a funded EVM wallet
400 `invalid transfer input`	You sent `_simulate_web3` with a live key	Remove it
Faucet USDC does not show on an EVM sandbox wallet	EVM sandbox wallets show the sandbox test dollar	See Fund wallets during testing
`balance_before` and `balance_after` repeat on the rows	A known sandbox difference	Read the wallet balance instead