werkzeug.exceptions.BadRequestKeyError: 400 Bad Request: The browser sent a request that this server could not understand. KeyError: 'newusername'

Question

# Route: User Registration
@app.route('/register', methods=['GET', 'POST'])
def register():
    newusername = request.form['newusername']
    userid = request.form['personid']    
    surname = request.form['surname']    
    gender = request.form['gender']
    section = request.form['section']
    designation = request.form['designation']
    userimagefolder = 'static/faces/'+newusername+'_'+str(userid)
    if not os.path.isdir(userimagefolder):
        os.makedirs(userimagefolder)
    i, j = 0, 0
    cap = cv2.VideoCapture(0)
    while 1:
        _, frame = cap.read()
        faces = extract_faces(frame)
        for (x, y, w, h) in faces:
            cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 0, 20), 2)
            cv2.putText(frame, f'Images Captured: {i}/{nimgs}', (30, 30),
                        cv2.FONT_HERSHEY_SIMPLEX, 1, (255, 0, 20), 2, cv2.LINE_AA)
            if j % 5 == 0:
                name = newusername+'_'+str(i)+'.jpg'
                cv2.imwrite(userimagefolder+'/'+name, frame[y:y+h, x:x+w])
                i += 1
            j += 1
        if j == nimgs*5:
            break
        #cv2.imshow('Adding new User', frame)
        
        return render_template('register.html', success=f"User {newusername} {surname} registered successfully!")
    else:
        return render_template('register.html', error="No face detected. Please try again.")
        session.add(name)
        session.commit()
        return render_template('register.html')

I am trying to add a user but getting the stated error. I have shared my @Route code for user registration. Can anyone please provide their valuable guidance for resolving this issue.