How to pass access token url in authentication flow oauth2

i follow the authentication flow with oauth2.0.
As in postman i can enter the
AUTH URL to start the process with a webpage and then authenticate on this external webpage with username and password.
I set the ACCESS TOKEN URL to my url which gets the code of the first step and receive a token.

Now i want to repeat this flow in my application, not in postman.

a) start AUTH URL to the external webpage and generate the code.
Which parameters must be set to handle later ACCESS TOKEN URL ?

b) This first section generates the code which i need for step c)

c) step b) must now use my ACCESS TOKEN URL and send the parameter code to receive then an new BEARER ACCESS TOKEN.

I have seen the console log, but i have never found my individual ACCESS TOKEN URL in this process, but with postman it works. I can get a BEARER TOKEN.