Hi @vijai,
I believe the correct API call would be something like:
https://ip_address/api/objects/predefinednetworkservices?order-by=faultInst.severity|desc&page=0&page-size=100
I found this answer on a discussion ASA REST API call limited to 100 where they link to this pagination section.
Of course, you may need to adjust or remove the part referencing faultInst.severity if that's what's needed.