> ## 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.

# Primary & Backup Funding 

Every Fluz account has a **default funding source** made up of two roles: a **primary** payment method and a **backup** payment method. Together they decide how a transaction is funded and what happens if the first attempt can't be completed.

| Role        | Shown in app as   | Must be a                        | Purpose                                                    |
| ----------- | ----------------- | -------------------------------- | ---------------------------------------------------------- |
| **Primary** | Preferred account | Bank account (ACH)               | The default funding source charged first for transactions. |
| **Backup**  | Backup card       | Bank card (debit/credit/prepaid) | Charged if the primary funding source can't be charged.    |

Each account has exactly **one primary and one backup** at a time. Selecting a new one replaces the previous selection for that role.

***

## How It Works

When a user makes a purchase, funds a virtual card, or deposits to their Fluz balance, Fluz charges the **primary** funding source first — by default, the preferred bank account over ACH.

Because ACH payments can settle over several days or fail, a **backup card** acts as the safety net:

* When a user pays via ACH, a temporary hold may be placed on the backup card for the transaction amount.
* If the ACH payment clears, the hold is released within 1–7 business days.
* If the ACH payment does not clear, the backup card is charged instead.

<Note>
  **A backup card must be on file before a transaction can complete.**

  Fluz requires a valid bank card as the backup payment method so a transaction can still be completed if the primary funding source fails. Without one, transactions that depend on ACH cannot be started.
</Note>

***

## Configuring Primary & Backup

<Note>
  **Primary and backup selection is managed in the Fluz app or web portal — not the API.**

  The API can add, update, and delete the underlying bank cards, and link or remove bank accounts. However, choosing **which** funding source is the primary or backup is only available in the Fluz app or web portal.
</Note>

### On the web

1. Open **Accounts and Cards** from the account menu (or go to `/accounts-and-cards`).
2. In the **Default funding source** section at the top of the page:
   * Select **Manage preferred account** to choose the bank account used as the default funding source.
   * Select **Manage backup card** to choose the bank card charged if the preferred account can't be.
3. Your selection is saved immediately.

### On mobile

1. Open the menu and tap **Accounts and Cards**.
2. Under **Default funding source**, tap **Manage preferred account** or **Manage backup card**.
3. Choose from your linked funding sources. Your selection is saved immediately.

If you don't yet have an eligible funding source, the app will prompt you to add one first — a bank account for the preferred account, or a bank card for the backup.

***

## What Can Be Done via API vs. App / Web

| Task                                             | API | App / Web |
| ------------------------------------------------ | --- | --------- |
| Add, update, or delete a **bank card**           | ✓   | ✓         |
| Link or remove a **bank account** (Plaid)        | ✓   | ✓         |
| Set which funding source is **primary / backup** | ✗   | ✓         |

See [Bank Cards](/features/link-external-cards) and [Bank Accounts](/features/link-external-bank-accounts) for the funding source operations that are available through the API.

***

## Eligibility & Notes

* The **primary** payment method must be a linked bank account; the **backup** must be a bank card.
* **Business accounts** must complete KYB verification before funding sources — and therefore the default funding source — can be set.
* Some funding sources may be restricted for specific merchants or by account limits and won't be selectable as a default.

***

**Want to learn more?** Speak with our experts for more info or to request a demo.