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Your account has a single environment field — sandbox or live — set with Switch Environment and readable from your Login response. Every service call (creating accounts, transfers, transactions) operates against whichever environment your account currently holds — there’s no separate sandbox/live API base URL to switch between for these calls, and no separate credential per environment (see the token-lifetime caveat in Authentication).

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What’s different in sandbox

  • Funding: use Fund Sandbox Balance to top your test business balance up to a working threshold — instantly, no real money involved. There’s no live equivalent; a live balance is funded by real inbound transfers.
  • Interbank transfers to arbitrary accounts: sandbox Transfer Between Accounts only supports Rex’s own designated sandbox test accounts as a regular (non-Rex) beneficiary — sending to an arbitrary external account returns 400 REGULAR_ACCOUNT_NOT_SUPPORTED_IN_SANDBOX. Transfers between two Rex-issued accounts work normally.
  • Rate limits, error shapes, and every other endpoint behave identically in both environments — sandbox is not a stripped-down mock, it’s the same code path against test data.

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Going live

You can’t switch to live until your onboarding application is approved (onboarding_status: active) — see the Going Live Checklist. Attempting to switch earlier returns 403 NOT_ACTIVE. Once live, treat it exactly like production banking infrastructure, because it is one: real transfers move real money and can’t be undone the way a sandbox mistake can.

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A note on simulate-inward-credit

You may notice Simulate Inward Credit in this reference and expect it to be the sandbox testing tool for inbound transfers. It isn’t reachable in production at all, for any partner, regardless of your sandbox/live environment setting — it’s gated to Rex’s own internal staging environment. To simulate money arriving in your sandbox account, use Post a Manual Credit or transfer from your funded sandbox Master balance instead.