Proplem in sorting by invoices serial number !

Proplem in sorting by invoices serial number !

I got an issue with sorting the invoices in serial wise in Zoho invoices! 

I got the following serial;
J-123
J-124
J-125
J-126

When i try sorting by invoice serial this will be the result;
J-125
J-123
J-126
J-124

Please advise ASAP