Funding wallets

A funding wallet is the Safe smart account on a card’s chain that the card draws balance from. There is no credit line on the Sumvin side — value sitting in the funding wallet is what authorises a transaction. Funding wallets are live.

Why this exists

Card-network rails expect an account to draw from. For a crypto-funded card that account is an on-chain wallet, but partners need a stable Sumvin handle on it: which wallet backs which card, what’s in it, how to top it up, where to look at recent activity. The funding wallet binding gives partners that handle without forcing them to track the relationship between an issued card and its on-chain backing themselves.

How it works

Every card record has a linked_wallet_id pointing at the user’s funding wallet. That wallet is a Safe (the user’s smart-contract wallet) on the same chain as the card. Sumvin returns the Safe’s address on every card response as linked_wallet_address, and exposes a dedicated funding endpoint for richer detail and updates.

Card (external_id, status, …)
  └─ linked_wallet_id ──▶ Funding wallet (Safe)
                            └─ address ──▶ Safe contract on Sei

Launch chain

Sei (chain ID 1329) is the launch chain for cards. The Safe that backs a card is deployed on Sei, and balances surface in the card’s funding response from there. Multi-chain card backing is not exposed today — a card has exactly one funding wallet on one chain.

Funding the wallet

A partner funds a card by sending value to the funding wallet’s address. The wallet is a normal Safe — anything that can transfer to a Safe address (an on-ramp, a DEX, a transfer from another wallet) can fund the card. There is no Sumvin-side “deposit” call. Once value lands on-chain at the Safe address, it’s available as funding. The Atomic Money ramps product is the supported on-ramp path for converting fiat into the funding wallet’s chain assets.

To surface what the funding wallet currently holds, with USD valuations, read its balance summary. The wallet ID returned from card responses is the same ID those wallet endpoints accept.GET /v0/wallets/{wallet_id}/balances

Endpoints

Two endpoints expose the funding binding directly. Both use standard Juno JWT auth (x-juno-jwt).

Get card funding

GET /v0/card/{card_id}/funding Returns the funding configuration for a card — currently the linked wallet’s address and a configured flag indicating whether the card has a funding wallet linked at all.

curl https://api.sumvin.com/v0/card/card-3f9c…/funding \
  -H "x-juno-jwt: <token>" \
  -H "x-juno-orgid: <your-org-id>"

Response — 200 OK

{
  "id": "card-3f9c…",
  "source_type": null,
  "wallet_address": "0xE23c…E992",
  "fiat_account_id": null,
  "configured": true,
  "_links": {
    "self": { "href": "/v0/card/card-3f9c…/funding" },
    "card": { "href": "/v0/card/card-3f9c…" },
    "wallet": { "href": "/v0/wallets/wallet-…" },
    "wallet-assets": { "href": "/v0/wallets/wallet-…/assets" },
    "wallet-transactions": { "href": "/v0/transactions?wallet_id=wallet-…" },
    "card-transactions": { "href": "/v0/transactions?card_id=card-3f9c…" },
    "user": { "href": "/v0/user/me" },
    "update": { "href": "/v0/card/card-3f9c…/funding", "method": "PUT" }
  }
}

string

External card ID.

string | null

Address of the Safe backing the card. null if no wallet is linked.

boolean

Whether a funding wallet is currently linked to the card.

string | null

Funding source type. Reserved — not yet populated by the read endpoint.

string | null

Linked fiat account ID. Reserved for future fiat funding sources.

The _links block is the canonical entry point for everything you’d want to do with the funding wallet — read its assets, list its transactions, or pull recent card transactions filtered to it.

Update card funding

PUT /v0/card/{card_id}/funding Accepts a funding source declaration. Changing a card’s funding source is in private preview: the endpoint accepts and validates a funding-source declaration and returns configured: false with message: "Funding configuration coming soon" until funding-source switching is available.

This endpoint is a stub today. The route accepts and returns the payload shape so client integrations can be built against it, but the funding source change is not persisted. Treat the linked wallet returned by the card read (or its funding endpoint) as the authoritative funding source.PUT /v0/card/{card_id}/funding — Stub; not persisted.GET /v0/card/{card_id} — Authoritative card record.

The accepted request shape:

string

required

One of wallet or fiat.

string

Required when source_type is wallet. The address of an existing user wallet to use as the funding source.

integer

Required when source_type is wallet. Must match the chain of the wallet at wallet_address.

string

Reserved for source_type=fiat.

Reading balance and activity

The funding response surfaces HAL links into the wallets and transactions APIs. The two most useful flows: Current balance

curl https://api.sumvin.com/v0/wallets/{wallet_id}/balances \
  -H "x-juno-jwt: <token>" \
  -H "x-juno-orgid: <your-org-id>"

Returns total assets held in the funding wallet with USD valuations. See the wallets guide for the full response shape. Card transactions

curl "https://api.sumvin.com/v0/transactions?card_id=card-3f9c…" \
  -H "x-juno-jwt: <token>" \
  -H "x-juno-orgid: <your-org-id>"

Returns transactions associated with the card. Pair with ?wallet_id={wallet_id} to filter by the funding wallet directly.

Errors

Funding endpoints reuse the card error codes. See Card management API → Errors for the full list. The two you’ll see at this surface:

Code	Status	Meaning
`CRD-404-001`	404	Card not found
`CRD-403-001`	403	Card belongs to a different user

Card issuing overview
Card management API
Wallets guide — Safe creation, chain selection, balances
Safes and identity — why a Safe and not an EOA
Atomic Money ramps — supported on-ramp into the funding wallet
Funding wallet (glossary)
Issue a card quickstart
Crypto wallet card use case

Introduction

Quickstarts

Guides

Product Guides

API Reference

Why this exists

How it works

Launch chain

Funding the wallet

Endpoints

Get card funding

Update card funding

Reading balance and activity

Errors

​Why this exists

​How it works

​Launch chain

​Funding the wallet

​Endpoints

​Get card funding

​Update card funding

​Reading balance and activity

​Errors

​Related

Why this exists

How it works

Launch chain

Funding the wallet

Endpoints

Get card funding

Update card funding

Reading balance and activity

Errors

Related