Writing to a collection in MongoDB Atlas with JS server code

I need to rebuild the JS (server) code to write to a DB collection in MongoDB Atlas.

Since I am encountering some problems on the way, I decided to write this post and see if someone could give me some help by having a new look at it.

First, here is how the collection looks:

_id: 6501df383452b6a687eb89c6channelID: "ENR6318ahecz"voiceRecordID: "6501df352839b6a687eb89c4"timeStamp: 1694676496005_id: 6501df783439b6a687da89cachannelID: "ENR6318ahecz"voiceRecordID: "6501df712219b6a687eb89c8"timeStamp: 1691921560338.....

I have this scheme working in TypeScript code, to access (by reading) the collection:

    const speakSchema = new Schema({        channelID: {            type: String,            required: true        },        voiceRecordID: {            type: String,            required: true        },        timeStamp: {            type: Number,            required: true        }    })    interface SpeakDoc extends Document {        channelID: string        voiceRecordID: string        timeStamp: number    }    interface SpeakModel extends Model<SpeakDoc> {}    const theModel = (models && models.Voice) ? (models.Voice as SpeakModel) :                                            mongoose.model<SpeakDoc, SpeakModel>                                                    ('Voice',speakSchema,'mycollection')

Then I have code like the one below to read the collection:

    await connectMDB()    try {        const theResult = await theModel        .find({channelID:channel})        return theResult    } catch (error) {        console.error("Error in Read-Function:", error);        throw error; // Rethrow the error to propagate it.    }

All the above works perfectly for now.

Next comes the problem. I need to be able to insert new records in the collection using JS. The code is in express server.

Here is what I have at this point, but it is not working:

    ....    const {Schema,model} = mongoose;    const vxSchema = new Schema({      channelID: String,      voiceRecordID: String,      timeStamp: Number    },    {        versionKey: false         /* This gets rid of the "__v: 0" that is        otherwise added to the collection. */    });    const VxIns = model('VxIns', vxSchema);    .....    function saveAudioToGridFS(audioBlob) {        return new Promise((resolve, reject) => {            const gridFSBucket = new mongoose.mongo.GridFSBucket(conn.db),                        upldName = getAudioName()            const writeStream = gridFSBucket.openUploadStream(upldName);            writeStream.on('close', (file) => {                if (file !== undefined) {                    resolve(file._id); // Return the GridFS file ID                }            });            writeStream.on('finish', (file) => {                if (file !== undefined) {                    resolve(file._id); // Return the GridFS file ID                }            });            writeStream.on('error', (error) => {                reject(error);            });        // Convert the Blob into a readable stream using streamifier        const readableStream = streamifier.createReadStream(audioBlob);        // audioBlob.pipe(writeStream);        readableStream.pipe(writeStream);        });    } /* End of saveAudioToGridFS */    server.post('/upload', async (req, res) => {        try {            if (!req.body.audio) {                return res.status(400).json({ message: 'No audio data uploaded.' });            }            console.log("Before saveAudioToGridFS")            const audioBuffer = Buffer.from(req.body.audio, 'base64'),                        fileId = await saveAudioToGridFS(audioBuffer);            console.log("fileId=",fileId)            // Create a new VX object:            const newRcd = new VxIns({                channelID:req.body.channel,                voiceRecordID:fileId,                timeStamp: new Date().getTime()            });            // Insert the newRcd in our MongoDB database            await newRcd.save();            res.json({ fileId });        } catch (error) {            console.error(error);            res.status(500).json({                message: 'An error occurred during upload.',                error: JSON.stringify(error)            });        }    });

Can someone see at a glance what is, or what could be, wrong in this last chunk of code ? Knowing that the first presented TypeScript code is working.

P.S. I just noticed that the call to saveAudioToGridFS, while saving data in the database as expected does not return the fileId as it should.