Microsoft Graph Pre-Authorize integration is not functioning

I was trying integrating MS GRAPH for my Bot for sending mail,
i was using ‘Pre-authorize the Integration’
1. for System its gets Authorize i am getting message as “Authorization Success”
but then it stuck,


and when i tried to save it it shows “please authorize system oauth”

2. When i go for Custom (created OAuthv2 with all the correct credentials)

it Got Redirected to MS page and then went into infinite Loading…

Can Someone Help me on this , why this is happening?