I am a developer and I want to integrate okta oauth in my application but I have some confusion and I am missing something to implement it properly.

I have one developer account of okta and I have saved client_id and client_secret in configuration. Now, I have 2 resource owners(who own the data) of okta and they want to give access of their data to my developer app so my app can read data from their account using access token but I am not able to do that so can some please guide me to implement it with proper details?

Below are the details which I have implemented till now:

My authorize URL for getting authorization code is

auth code URL :- https://dev-92284977.okta.com/oauth2/v1/token

dev client_id :- xxxxxxxxxxx_u2183

dev secret_id :- xxxxxxxxx_98yd9

Now it opens the prompt to enter signing credentials and when I try to sign in with resource owner credentials then it shows me unable to sign in error. It only allows me to login with developer account credentials so am I missing something or what should I have to correct over here?