atob decode is not working when string is starts with slash [closed]

I am trying to decode the string value using atob. The value of string which I got from the backend starts with . Now string is getting it to \.

In the attached screenshot when value base64String passed to atob it shows single and in the parameter shows the value with \. When execute console.log('x4c693...') in browser console it works but when executed console.log('\x4c693...') it fails with error saying DOMException: Failed to execute 'atob' on 'Window': The string to be decoded is not correctly encoded.

How to decode this type of string.