The Procore API reference states that the only http callback URI that is acceptable is "http://localhost". The sample app uses a callback URI of "http://localhost:3000/users/home" which is rejected by the Procore API at runtime. In order to fix this I had to add the code below into the oath_main file:

callbackapp = Flask(__name__)

@callbackapp.route('/',methods=["GET", "POST"])
def app_callback1():
    if request.method == "GET":
        if session.get('bool') is False:
            code = request.args.get('code')
            cburl= f'{REDIRECT_URI}?code={code}'
    return redirect(cburl)

and then run a separate python script to run it before spinning up the main server on port 3000, coded as follows:

from oauth_main import callbackapp

#------- Runs the callback application ------
callbackapp.run(debug=True, port=80)

I then had to change all functions that were sending a callback URI to Procore to use http://localhost, which I just hardcoded since it isn't optional.
these functions were:

• make_authorization_url()
• get_token(code)

The issues are twofold:

1. The Procore-Official sample app doesn't follow Procore's requirements for callback URIs and therefore is not a currently functioning sample
2. The Procore API does not recognize endpoints at http://localhost/[ENDPOINT HERE] or on other ports. This should be changed to allow any endpoint or port on the local machine - it is far too limiting and clumsy to have to listen on port 80 while running everything else on a different port.