Get Outlook Mail Messages activity error

I want to get all unread mails containing excel attachments with them.
But “Filter” property is not working with “.xlsx”, it is throwing the error (PFA screenshot).
Please let me know how can I resolve this. Thank you.

you cannot use filter like this.
once you read all unread mails have a loop for each mail message then inside check mailmessage contains attachment.
then check attachment count and check for each attachment if attachment name contains .xlsx and you can filter and save the attachments as well.