curl -X POST "https://api.cryptomate.me/management/clients/client_a1b2c3d4-e5f6-4a7b-8c9d-0e1f2a3b4c5d/providers" \
  -H "x-api-key: $CRYPTOMATE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "provider": "BRIDGE",
    "customer_id": "cust_ext_xyz789"
  }'

{
  "id": "cpc_abc123",
  "client_id": "client_a1b2c3d4-e5f6-4a7b-8c9d-0e1f2a3b4c5d",
  "provider": "BRIDGE",
  "customer_id": "cust_ext_xyz789",
  "status": "active",
  "created_at": "2026-04-15T10:30:00",
  "updated_at": "2026-04-15T10:30:00"
}

{
  "code": "VAL",
  "message": "Client already has a customer ID for provider BRIDGE"
}