Error while calling the send_file function from another file in python flask | RuntimeError: Working outside of request context

Question

Greetings stack overflow community, I am currently working on a flask app and I am trying to retrieve a file from a helper function with the send_file method in flask.

I have a route that goes like so:

@app.route("/process",methods=['GET','POST'])
def do_something():
    process = threading.Thread(target=function_name,args=[arg1,arg2])
    process.start()
    return render_template("template.html")

The function_name (which is on a different file) function is suposed to return a file like so

def function_name():
        filename = 'ohhey.pdf'
        return send_file(filename,as_attachment=True,cache_timeout=0)

When I run my app like this I get the following error

RuntimeError: Working outside of application context.

This typically means that you attempted to use functionality that needed
to interface with the current application object in some way. To solve
this, set up an application context with app.app_context().  See the
documentation for more information.

So I try to change the function for the following:

def function_name():
        filename = 'ohhey.pdf'
        with app.app_context():
            return send_file(filename,as_attachment=True,cache_timeout=0)

and get this new error

RuntimeError: Working outside of request context.

This typically means that you attempted to use functionality that needed
an active HTTP request.  Consult the documentation on testing for
information about how to avoid this problem.

so I try the following:

def function_name():
        filename = 'ohhey.pdf'
        with app.test_request_context():
            return send_file(filename,as_attachment=True,cache_timeout=0)

After making this final change my app doesn't return a file or an error. I appreciate your help.