Sponsored Transactions

The Andamio API builds transactions. Who pays the fees is your choice. By default the user's own wallet pays, as described in Transaction Handling. On eight course routes you can name a sponsor wallet you run instead, so your users never need ADA.

Andamio does not pay the fees of a transaction built through the Andamio API. Your sponsor wallet does.

Want Andamio to sponsor for you?

That is Andamio Issuer, a separate product with its own key, the Andamio Issuer API key. Andamio builds, sponsors and submits Issuer transactions. An Andamio Issuer API key gets a 403 on every Andamio API transaction build route.

Sponsored Routes

These eight routes accept an optional sponsor_data object. Each returns the same response as a self-funded build.

Request	Response
`POST /api/v2/tx/global/user/access-token/mint`	`{ unsigned_tx }`
`POST /api/v2/tx/instance/owner/course/create`	`{ course_id, unsigned_tx }`
`POST /api/v2/tx/course/owner/teachers/manage`	`{ unsigned_tx }`
`POST /api/v2/tx/course/teacher/modules/manage`	`{ unsigned_tx }`
`POST /api/v2/tx/course/teacher/assignments/assess`	`{ unsigned_tx }`
`POST /api/v2/tx/course/student/assignment/commit`	`{ unsigned_tx }`
`POST /api/v2/tx/course/student/assignment/update`	`{ unsigned_tx }`
`POST /api/v2/tx/course/student/credential/claim`	`{ unsigned_tx }`

The project routes and the other transaction routes build self-funded transactions only.

The sponsor_data Object

sponsor_data names the sponsor wallet and two UTxO references. The two references come from getStaticInfo() in the utxos.dev SDK, which you call yourself. Do not pick arbitrary UTxOs: the sponsorship contract requires these exact references.

Field	Required	Description
`sponsor_address`	Yes	Bech32 address of the sponsor wallet that pays the fees
`static_utxo_ref`	Yes	UTxO reference (`txhash#index`) from `getStaticInfo()`
`collateral_utxo_ref`	Yes	Collateral UTxO reference (`txhash#index`) from `getStaticInfo()`
`access_token_receiver`	Mint only	Bech32 address of the user's wallet that receives the access token. Must differ from `sponsor_address`

On the seven course routes, add sponsor_data to the body you would send for a self-funded build:

{
  "alias": "student1",
  "course_id": "ff80aaaf03a273b8f5c558168dc0e2377eea810badbae6eceefc14ef",
  "slt_hash": "a1b2c3d4...",
  "assignment_info": "My submission",
  "sponsor_data": {
    "sponsor_address": "addr1...",
    "static_utxo_ref": "<txhash>#0",
    "collateral_utxo_ref": "<txhash>#1"
  }
}

On access-token/mint, send either initiator_data (self-funded) or sponsor_data (sponsored). Sending neither or both returns a 400.

After the Build

The route returns an unsigned transaction. The Andamio API has no submit route: the sponsor's signature, the user's signature and submission to Cardano are yours. After you submit it, register it with POST /api/v2/tx/register and monitor it exactly as in Transaction Handling.

Sponsor signing is not documented here

The Andamio API contract does not describe how the sponsor wallet adds its signature to a sponsored build. It names only the utxos.dev sponsorship contract and the SDK's getStaticInfo(). Follow the utxos.dev documentation for that step.

Errors

A sponsored build returns the same errors as a self-funded build, plus these:

Status	Meaning
`400 Bad Request`	On `access-token/mint`: neither or both of `initiator_data` and `sponsor_data`, or `access_token_receiver` equals `sponsor_address`.
`403 Forbidden`	The request used an Andamio Issuer API key. Andamio API transaction build routes take a developer key.

Andamio keeps no sponsorship quota for these builds. Your tier's normal API quotas still apply.

Next Steps

Transaction Handling: The build, sign, submit, register lifecycle
API Keys: Get a developer key
Error Handling: Recovery patterns