Using Flask send_to_directory, not being able to download the correct file - python-3.x

Question

I am working on a Flask app that processes input and creates a file at the end. I am trying to download that file using send_to_directory().
Route:
#app.route('/file-diff', methods=['GET','POST'])
def file_diff():
if request.method == "POST":
results = process_request(ip_a=request.form.get("ip_a"), chk1=request.form.get("chk1"), ip_b=request.form.get("ip_b"), chk2=request.form.get("chk2"))
path,filename = os.path.split(results)
print(app.config["DOWNLOADS"])
# outputs - /cache/app_bd/app/downloads
print("Path to file = {}".format(path))
# outputs - Path to file = /cache/app_bd/app/downloads
print("Filename = {}".format(filename))
# outputs - Filename = diff_results
try:
return send_from_directory(directory=app.config["DOWNLOADS"], path=filename, as_attachment=True)
except FileNotFoundError:
abort(404)
return redirect(request.url)
return render_template("file_diff.html")
Directory Structure:
:/cache/app_bd# ls -lR
drwxr-xr-x 7 root root 4096 Apr 13 13:00 app
-rw-r--r-- 1 root root 783 Apr 13 16:29 config.py
-rw-r--r-- 1 root root 174 Apr 11 16:22 requirements.txt
-rw-r--r-- 1 root root 92 Apr 13 12:48 run.py
./app:
-rw-r--r-- 1 root root 309 Apr 13 12:14 __init__.py
-rw-r--r-- 1 root root 2024 Apr 13 15:35 file_utils.py
drwxr-xr-x 2 root root 4096 Apr 13 13:02 downloads
drwxr-xr-x 2 root root 4096 Apr 12 16:13 scripts
drwxr-xr-x 6 root root 4096 Apr 13 13:00 static
drwxr-xr-x 2 root root 4096 Apr 12 16:11 templates
-rw-r--r-- 1 root root 1717 Apr 13 17:05 views.py
./app/downloads:
-rw-r--r-- 1 root root 85008 Apr 13 17:05 diff_results
The above code works but downloads file_diff.html itself. The expected file to download is diff_results.
What was tried?
Setting path="app/downloads and filename=filename inside send_to_directory()
Setting send_from_directory(app.config["DOWNLOADS"], filename=filename, as_attachment=True)
Setting send_from_directory(app.config["DOWNLOADS"], filename, as_attachment=True)
None of the above changes helped in downloading the correct file (diff_results).
Is it mandatory to have a route like -
#app.route('/download/<filename>', methods = ["GET", "POST"])
def download(filename):
Am I missing something?