Datatable returns all the data when server side is set to true - datatables

Question

I have the following code where I want to use server side to lazy load my data. My goal is to display 10 records per page. The rest of the data should be loaded as and when the user clicks on a particular page.
What's happening now is that the datatable displays all the records at once. Can someone help me fix this issue?
var table = $("#members").DataTable({
"processing": true,
"serverSide": true,
paging: true,
"pagingType": "full_numbers",
"iDisplayLength": "10",
"length": "10",
ajax: {
url: "/api/members",
dataSrc: "",
},
columns: [
{
data: "cardNumber"
},
{
data: "registrationDate",
},
{
data: "fullName",
},
{
data: "address"
},
{
data: "phoneNumber"
},
{
data: "email"
}
]
});
Here's the API code:
// GET /api/members
public IEnumerable<MemberDto> GetMembers(string query = null)
{
var membersQuery = _context.Members.ToList();
if (!String.IsNullOrWhiteSpace(query))
membersQuery = membersQuery.Where(c => c.FullName.Contains(query.ToUpper())).ToList();
var memberDtos = membersQuery.ToList()
.Select(Mapper.Map<Member, MemberDto>);
return memberDtos;
}