What does Fee waived mean?

[L1A_asp]

My daughter's I131 receipt was sent to attorney and also to us.But our postmn retruned it undelivered to USCIS.USCIS triggered an alert email saying looks like ur address has changed pls contact us.We did and told no change in address.

Today we got I-797C saying Notice Type : Receipt Notice Fee Waived

Does it mean they are sending the receipt notice again or its the next step in I131?
Me and My spouse haven't received this for our I131