curl --request GET \
  --url https://api.upwell.com/api/rest/document_reference_specifications

{
  "documentReferenceSpecifications": [
    {
      "createdAt": "<unknown>",
      "customer": {
        "id": "<string>",
        "name": "<string>"
      },
      "customerId": "<string>",
      "formatRegex": "<string>",
      "id": "<string>",
      "name": "<string>",
      "nameRegex": "<string>",
      "tenantId": "<string>",
      "updatedAt": "<unknown>"
    }
  ]
}