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Attestations are required to submit transfers onchain. Most users will want to leverage Union’s hosted service, although onpremise is also available for enterprise clients. Requesting an attestation requires a valid API_KEY, and submitting both the unspendableAddress and beneficiary. 
curl -X POST 'https://attestor.union.build/functions/v1/attest' \
    -H 'Content-Type: application/json' \
    -H 'x-api-key: $API_KEY' \
    -d '{
      "unspendableAddress": "0x6E908eA716689c6ae2EC7A374781ae5C078D688B",
      "beneficiary": "0x3d2F673B11f62b787faa1ef2871E2408aE22b717"
    }'
The service will return a signed attestion required to submit transfers 
{
	"id": "e05ae9d8-067a-4ced-8f22-1ff4f8bfce33",
	"hash": "0x1c16ab366fc0694d16c63d0077ca102abcb7453fc78eb7d0f71928e28f1325b9",
	"signature": { 
		"r": "0x282fef222b695aca77bf970b6b3c54569ad2d8da230d4f113b4a7884380ac71c",
		"s": "0x2cca5c94a904f0c031c8485c2ae60c6b7bb086d15056f4a08f3a9f33e2ec844f",
		"v": 27
	},
	"signerAddress":"0xDB2CEf6d390d344B46757e2cEe24447A3bcC808f"
}
The returned id is a UUID, which can be stored for internal record keeping.