React native – Filesystem doesn't save my file and throws error

I am trying to save a set of time lapse to an Excel file in expo react native app which I am building. When I click save button, it throws this error

[Unhandled promise rejection: Error: Call to function ‘ExponentFileSystem.writeAsStringAsync’ has been rejected.]

I am using android device.

I look all over google, but I can’t find a solution for this issue. Does anyone have any idea how to solve this ?

Here is my code for the function that saves the file:

const writeArrayToExcel = async (dataArray) => {
    const resultsMade = [["lap", "time"]];
    dataArray.map((lapTime, index) => {
        const lapName = `${lapWord} ${index + 1}`;
        const valLap = `${displayTime(lapTime).hours}:${displayTime(lapTime).minutesSeconds}:${displayTime(lapTime).centiseconds}`;
        resultsMade.push([lapName, valLap]);
    })

    let wb = XLSX.utils.book_new();
    let ws = XLSX.utils.aoa_to_sheet(resultsMade);

    XLSX.utils.book_append_sheet(wb, ws, 'Sheet1');
    
    const base64 = XLSX.write(wb, { bookType: 'xlsx', type: 'base64' });

    const currentDate = new Date();
    const formattedDate = `${currentDate.getFullYear()}-${(currentDate.getMonth() + 1).toString().padStart(2, '0')}-${currentDate.getDate().toString().padStart(2, '0')}_${currentDate.getHours().toString().padStart(2, '0')}-${currentDate.getMinutes().toString().padStart(2, '0')}-${currentDate.getSeconds().toString().padStart(2, '0')}`;

    const filename = FileSystem.downloadDirectory + `Stopwatch-${formattedDate}.xlsx`;
    FileSystem.writeAsStringAsync(filename, base64, {
        encoding: FileSystem.EncodingType.Base64
    }).then(() => {
        //Sharing.shareAsync(filename);
    });
};

const exportToExcel = () => {
    writeArrayToExcel(results);
};