curl --request PATCH \
  --url https://api.syntage.com/shareholders/{shareholderId}/relations/{relationId} \
  --header 'Content-Type: application/json' \
  --header 'X-API-Key: <api-key>' \
  --data '{
  "shares": 1500.5
}'

{
  "@id": "/shareholders/91ab5678-1234-5678-9abc-def012345678/relations/82cd9012-3456-7890-abcd-ef1234567890",
  "@type": "ShareholderRelation",
  "id": "82cd9012-3456-7890-abcd-ef1234567890",
  "link": "/entities/91ab5678-1234-5678-9abc-def012345678",
  "shareholder": {
    "@id": "/shareholders/91ab5678-1234-5678-9abc-def012345678",
    "@type": "<string>",
    "id": "91ab5678-1234-5678-9abc-def012345678",
    "name": "JUAN MANUEL PEREZ GONZALEZ",
    "type": "physical",
    "rfc": "PEIC211118IS0",
    "relations": [
      {}
    ],
    "entity": "/entities/91ab5678-1234-5678-9abc-def012345678",
    "createdAt": "2020-01-01T12:15:00.000Z",
    "updatedAt": "2020-01-01T12:15:00.000Z"
  },
  "relationType": "shareholders",
  "sources": [
    {
      "@id": "/shareholders/91ab5678-1234-5678-9abc-def012345678/relations/82cd9012-3456-7890-abcd-ef1234567890/sources/73de0123-4567-8901-bcde-f23456789012",
      "@type": "ShareholderRelationsSource",
      "id": "73de0123-4567-8901-bcde-f23456789012",
      "relation": {},
      "shareholder": {
        "@id": "/shareholders/91ab5678-1234-5678-9abc-def012345678",
        "@type": "<string>",
        "id": "91ab5678-1234-5678-9abc-def012345678",
        "name": "JUAN MANUEL PEREZ GONZALEZ",
        "type": "physical",
        "rfc": "PEIC211118IS0",
        "relations": [
          {}
        ],
        "entity": "/entities/91ab5678-1234-5678-9abc-def012345678",
        "createdAt": "2020-01-01T12:15:00.000Z",
        "updatedAt": "2020-01-01T12:15:00.000Z"
      },
      "sourceName": "manual",
      "sourceId": "64ef1234-5678-9012-cdef-345678901234",
      "shares": 1500.5,
      "createdAt": "2020-01-01T12:15:00.000Z",
      "updatedAt": "2020-01-01T12:15:00.000Z"
    }
  ],
  "shares": 1500.5,
  "totalShares": 10000,
  "ownership": 0.15,
  "createdAt": "2020-01-01T12:15:00.000Z",
  "updatedAt": "2020-01-01T12:15:00.000Z"
}