Resolution

Navigate back to the CSS hosting page
Click Client Configuration then Edit
Click on Payment Services
Click Change on the payment vendor the client is using
Under the Postback URL verify that the URL does not contain CSS in all caps
Example URL with incorrect formatting: https://selfservice.xxxxxxxxx.gov/CSS/PaymentConfirmation.ashx?svc=0&client=1&
Update the Postback URL to have css in lowercase.
Example URL with correct formatting: https://selfservice.xxxxxxxxx.gov/css/PaymentConfirmation.ashx?svc=0&client=1&
Note: for a test or train environment the url may say CSSTest / CSSTrain. This should become csstest / csstrain.
Click Update

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