getWithPopup hangs up

I’m using @okta/okta-auth-js client for signing in to my website with Okta users.

            const authOktaClient = new OktaAuth({
                issuer: oktaData.issuer,  
                clientId: oktaData.clientId,
                redirectUri: beUrl + '/okta/callback`,
                responseType: 'code',
                pkce: false

                prompt: 'login'
            }).then(res => {
                let tokens = res.tokens;
                cb(null, tokens);
            }, err => {

At the beginning I received an authorization code request form Okta to my BE and successfully converted it to the Okta access_token. For all sequential calls I see an Okta popup with hardcoded username that cannot be changed and when I enter a password the Okta completely bypasses my BE, redirects to the blank page and hangs up there:

Cleaning browser cache doesn’t help.

P.S. On the other hand the authOktaClient.token.getWithRedirect flow reaches the BE and after that completes well.

What is BE? Is that an external identity provider?

BE - this is our BackEnd server with express.js
When I’m using Code Authorization or Implicit flows the Okta request doesn’t reach it at all but redirect to the page that has some window.postMessage commands. It looks like the communication between the main SDK script and the opened popups doesn’t work.