About ITAX CRN Expiry

We made an Online Advance Tax Payment on our PAN recently and w.r.t that received the following message from ITAX:

"Your CRN XXXXX dated XX/XX/XXXX is valid till XX/XX/XXXX.
To ensure CRN does not expire, please make remittance of tax within this date."

What does this mean? And how are we to respond? Please note that the payment is already done and we are abroad.

Thank you.