Tudo bem também.
O atributo referente às parcelas se chama installments, veja um exemplo de consumo com ele sendo utilizado:
{
"payment": {
"credit_card": {
"customer": {
"name": "Gorbadoc Oldbuck",
"cpf": "94271564656",
"email": "
[email protected]",
"birth": "1990-08-29",
"phone_number": "5144916523"
},
"installments": 1,
"payment_token": "",
"billing_address": {
"street": "Avenida Juscelino Kubitschek",
"number": "909",
"neighborhood": "Bauxita",
"zipcode": "35400000",
"city": "Ouro Preto",
"complement": "",
"state": "MG"
}
}
}
}