> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fluz.app/llms.txt
> Use this file to discover all available pages before exploring further.
# Manage Virtual Card Funding Sources
> Choose what pays for a virtual card — a spend account, an external bank account, rewards, prepayment balance, or a combination.
Every virtual card draws from something when it is charged. Fluz gives you four sources, and a card can use more than one at a time.
**By default, cards draw from three balances, not one.**
If you set a `userCashBalanceId` and nothing else, the card can still reach into the rewards balance and the prepayment balance when they have funds. That is the default and it is deliberate — but it means a card you believed was ringfenced to one budget can spend money from elsewhere on the account.
To isolate a card to a single spend account, you must explicitly set `usePrepaymentBalance: false` and `useRewardsBalance: false`. See [Isolating a card](#isolating-a-card-to-one-spend-account).
***
## The two layers
Funding is configured in two independent layers. Getting them confused is the most common source of unexpected declines.
`primaryFundingSource` is either `FLUZ_BALANCE` (money already held on the account) or `BANK_ACCOUNT` (pulled from a linked external bank via ACH). Defaults to `FLUZ_BALANCE`.
When the primary source is `FLUZ_BALANCE`, the card can draw from a specific spend account, the prepayment balance, and the rewards balance. `userCashBalanceId`, `usePrepaymentBalance`, and `useRewardsBalance` control which.
***
## The four options
### 1. A specific spend account
Spend accounts are named sub-ledgers on the account — "Team Travel", "Marketing", "Payouts". Nominate one with `userCashBalanceId` and the card draws from that balance rather than the account's general cash balance.
```json theme={null}
{
"primaryFundingSource": "FLUZ_BALANCE",
"userCashBalanceId": "b1155504-ad30-4b2f-873d-b8795277b128"
}
```
This is the right default for anything that needs to be budgeted, attributed, or reconciled separately. To create additional spend accounts, see [Create Spend Accounts](/features/create-spend-accounts); to list the ones you already have and read their balances, see [Get Spend Accounts](/features/get-spend-accounts).
### 2. An external bank account
Set `primaryFundingSource: BANK_ACCOUNT` and supply `bankAccountId`. Fluz pulls from the linked account after the card is spent, so you do not have to pre-fund a balance.
```json theme={null}
{
"primaryFundingSource": "BANK_ACCOUNT",
"bankAccountId": "432bff1b-89b2-4df8-8298-0b6ae5e92945"
}
```
`bankAccountId` is **required** when `primaryFundingSource` is `BANK_ACCOUNT`. Omitting it fails the request with `ARG-0001`.
Bank accounts are linked through Plaid — see [Linking Bank Account via Plaid](/features/link-via-plaid) and [Manage linked bank accounts](/features/link-external-bank-accounts). To read the accounts already linked, use [View Funding Sources](/features/view-funding-sources).
### 3. Prepayment balance
The prepayment balance is a non-withdrawable balance usable toward gift card and virtual card purchases. It contributes automatically unless you switch it off.
```json theme={null}
{
"usePrepaymentBalance": false
}
```
**This balance goes by several names.** It appears as `usePrepaymentBalance` on card input, as `giftCardCashBalance` in the [`getWallet`](/features/check-account-balance) response, and as "prepaid (gift card) balance" in prose. They are the same pool of money.
### 4. Rewards balance
Accumulated cashback and bonus rewards. Like the prepayment balance, it contributes by default.
```json theme={null}
{
"useRewardsBalance": false
}
```
Leaving rewards on maximizes the use of money already earned. Switching it off keeps rewards intact for withdrawal and makes card spend attributable to a single budget — which is usually what a business or platform program wants.
***
## Reference table
| Field | Type | Default | Controls |
| :--------------------- | :------------------------- | :------------- | :----------------------------------------------------------------- |
| `primaryFundingSource` | `VirtualCardFundingSource` | `FLUZ_BALANCE` | Whether the card pulls from Fluz-held funds or an external bank. |
| `bankAccountId` | `UUID` | — | Which linked bank account. Required when source is `BANK_ACCOUNT`. |
| `userCashBalanceId` | `UUID` | — | Which spend account the card draws from. |
| `usePrepaymentBalance` | `Boolean` | `true` | Whether the prepayment balance may contribute. |
| `useRewardsBalance` | `Boolean` | `true` | Whether the rewards balance may contribute. |
***
## Isolating a card to one spend account
The complete configuration for a card that can only ever spend from one nominated budget:
```json theme={null}
{
"input": {
"idempotencyKey": "07df5653-43a8-4532-9881-3ab5857bbe13",
"offerId": "ed669305-5e43-40a0-9a25-7a15ed174628",
"spendLimit": 150.00,
"primaryFundingSource": "FLUZ_BALANCE",
"userCashBalanceId": "b1155504-ad30-4b2f-873d-b8795277b128",
"usePrepaymentBalance": false,
"useRewardsBalance": false
}
}
```
All three of `userCashBalanceId`, `usePrepaymentBalance: false`, and `useRewardsBalance: false` are required for true isolation. Setting the spend account alone is not enough.
***
## Reading what is available
Before issuing, check that the source you are about to nominate actually has funds. [`getWallet`](/features/check-account-balance) returns every balance and linked funding source in one call.
```graphql theme={null}
query {
getWallet {
bankAccounts { bankAccountId }
balances {
rewardsBalance { availableBalance }
cashBalance { availableBalance }
giftCardCashBalance { availableBalance }
userCashBalances(paginate: { limit: 20, offset: 0 }) {
userCashBalanceId
nickname
availableCashBalance
status
}
}
}
}
```
Use `availableCashBalance` rather than `totalCashBalance` — the total can include funds that are pending and not yet spendable.
***
## Changing funding after issuance
[`editVirtualCard`](/features/edit-virtual-card) accepts `primaryFundingSource` and `bankAccountId`, so you can move a card between Fluz balance and an external bank, or swap which bank account it pulls from.
```json theme={null}
{
"input": {
"idempotencyKey": "d3b07384-d9a0-4f1e-9b2c-7a5e8c1f2d64",
"virtualCardId": "07df5653-43a8-4532-9881-3ab5857bbe11",
"primaryFundingSource": "BANK_ACCOUNT",
"bankAccountId": "432bff1b-89b2-4df8-8298-0b6ae5e92945"
}
}
```
**Balance composition appears to be set at issuance only.** `userCashBalanceId`, `usePrepaymentBalance`, and `useRewardsBalance` are not in the published `EditVirtualCardInput`. If you need a card pointed at a different spend account, plan to issue a replacement rather than edit the existing card.
***
## Account-level defaults are a different thing
Fluz also has an account-wide primary and backup payment method, set with [`setPrimaryFundingSource`](/features/primary-and-backup-funding) and `setBackupFundingSource`. These are **not** the same as per-card funding:
| | Scope | Set with |
| :------------------------- | :------------------------------------------------------------ | :--------------------------------------------------- |
| **Per-card funding** | One virtual card | `createVirtualCard` / `editVirtualCard` |
| **Account primary/backup** | Account-wide default, used when nothing more specific applies | `setPrimaryFundingSource` / `setBackupFundingSource` |
The backup payment method exists to cover the case where the primary source cannot be charged. See [Primary & Backup Funding](/features/primary-and-backup-funding).
***
Add a new spend account to fund cards from.
Connect an external bank account for `BANK_ACCOUNT` funding.
Read every balance and linked source before issuing.
How funding differs on hosted open-loop cards.