When trying to add a new Twitter handle to a new Twitter account setup on Omnichannel, it failed to validate the authentication.
Each time I try to authenticate it fails with the message: “Something went wrong. Please try singing in again”

Ensure that you have meet up the prerequisites steps here Configure a Twitter Direct Message channel | Microsoft Docs

I found that the  Twitter channel Environment name in the Omnichannel did not match with the Dev environment label Twitter developer portal.

To solve this issue, the “Environment name” field must match with the Dev Environments in the twitter developer account.

Navigate to Dev Environments under Premium. In the Dev Environment, under Account Activity API/Sandbox the Dev environment label must match with the Environment name in the Omnichannel for Customer Service.