paad/action/action_horario.php

<?php
header('Content-Type: application/json');

$ruta = "../";
require_once("../include/bd_pdo.php");

extract($_POST);

$dias = array("domingo", "lunes", "martes", "miércoles", "jueves", "viernes", "sábado");
$horarios = $db
    ->get("fs_horario($periodo, $carrera, '$grupo', true)");

// get each id from $horarios (might be duplicate)

try {
    $horarios = array_map(function ($horario) use ($dias, $db) {
        $horario['profesores'] = array_map(
            fn ($profesor) =>
            $db->where("id", $profesor)->getOne("fs_profesor"),
            explode(",", substr($horario['profesores'], 1, -1))
        );
        $horario['dia'] = $dias[$horario['dia']];
        return $horario;
    }, $horarios);
} catch (Exception $e) {
    die(json_encode([
        "status" => "error",
        "message" => $e->getMessage(),
    ]));
}
?>
<?= json_encode([
    "status" => "success",
    "horario" => $horarios,
]) ?>