Check out a short video on you can use Apigee Edge's out of the box policies to set up OAuth 2.0 using the password grant type in minutes.
What client id and secret were used? Is it the values provided by backend authorization server or just key:secret generated in Apigee Developer portal?
@Vladyslav , Welcome to Apigee Community.
Yes, It's Key Secret displayed in Developer portal, Generated by Apigee Edge Management server.
Here's a lab exercise with code that allows you to try out the Password Grant flow yourself:
https://github.com/DinoChiesa/devjam3-20170405/tree/master/Labs/Appendix/API Security - Securing APIs with OAuth password grant
sorry. looks like a cut/paste issue. Try now?