DCS enabled VBCS page ends with error on loading

Content

We have a DCS enabled VBCS page. The page loads successfully for few seconds before erroring out with An unspecified error has occurred and upon inspection, we find this.

{
    "type": "abcs://proxy_problem/basic/credentialHeader",
    "title": "Missing credential",
    "detail": "The required Basic authentication credentials are not specified in the service connection.",
    "status": 400
}