The file name when I downloaded it was object object

Here is body request
Here is my code

fetch(`${proxy()}${dataUrlExport}`, {
      method: "POST",
      headers: {
        "content-type": "application/json",
        Accept:
          exportType === "excel"
            ? "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
            : "text/csv",
      },
      body: JSON.stringify(exportBody),
    })
      .then((res) => res.blob())

      .then((blob) => {
        if (exportType === "csv") {
          const bom = new Uint8Array([0xef, 0xbb, 0xbf]);
          const withBom = new Blob([bom, blob], { type: "text/csv" });
          blob = withBom;
        }
        const url = window.URL.createObjectURL(blob);
        ////////console.log(1300, url)
        const a = document.createElement("a");
        a.style.display = "none";
        a.href = url;

        const datetimeString = getCurrentDateTimeForFilename();

        const segments = page.page_title.split("/");
        const lastSegment = segments[segments.length - 1]; //tên
        const result = lastSegment.replace(/-/g, "");
       
        a.download =
          exportType === "excel"
            ? `DATA_${result.toUpperCase()}_${exportBody.criteria}_${datetimeString}.xlsx`
            : `DATA_${result.toUpperCase()}_${datetimeString}.csv`;

        document.body.appendChild(a);
        a.click();
        window.URL.revokeObjectURL(url);
        setLoadingExportFile(false);
        setSelectedFields([]);
        setSelectAll(false);

I want it to be included when I download the file name is exportBody.criteria: RF20243220001 but I get object

How do I get it and assign it to the filename?

tks guys