Como usar variaveis num POSTFIELD?

$curl = curl_init();

    curl_setopt_array($curl, array(
        CURLOPT_URL => 'https://pririrpaoduro-financeira.com.br/sim/calculo',
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_ENCODING => '',
        CURLOPT_MAXREDIRS => 10,
        CURLOPT_TIMEOUT => 0,
        CURLOPT_FOLLOWLOCATION => true,
        CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
        CURLOPT_CUSTOMREQUEST => 'POST',
        CURLOPT_POSTFIELDS =>'{
            "cpf" : "00000000000",
            "taxa" : 2.04,
            "tabela" : 38776,
            "parcelas" : [
                {
                    "dataRepasse_1": "01/08/2023",
                    "valor_1": 42.15
                },
                {
                    "dataRepasse_2": "01/08/2024",
                    "valor_2": 21.08
                },
                {
                    "dataRepasse_3": "01/08/2025",
                    "valor_3": 10.54
                },
                {
                    "dataRepasse_4": "01/08/2026",
                    "valor_4": 5.27
                },
                {
                    "dataRepasse_5": "01/08/2027",
                    "valor_5": 2.63
                },
                {
                    "dataRepasse_6": "01/08/2028",
                    "valor_6": 1.32
                },
                {
                    "dataRepasse_7": "01/08/2029",
                    "valor_7": 0.66
                },
                {
                    "dataRepasse_8": "01/08/2030",
                    "valor_8": 0.33
                },
                {
                    "dataRepasse_9": "01/08/2031",
                    "valor_9": 0.16
                },
                {
                    "dataRepasse_10": "01/08/2032",
                    "valor_10": 0.08
                },
                {
                    "dataRepasse_11": "01/08/2033",
                    "valor_11": 0.04
                },
                {
                    "dataRepasse_12": "01/08/2034",
                    "valor_12": 0.02
                }
            ]
        }',
        CURLOPT_HTTPHEADER => array(
            'Authorization: Bearer '. $bearer, 'Content-Type: application/json'),
    ));

    $response = curl_exec($curl);
    curl_close($curl);

    echo $response;