You aren't actually sending JSON. You are passing an object as the data, but you need to stringify the object and pass the string instead.
Your dataType: "json" only tells jQuery that you want it to parse the returned JSON, it does not mean that jQuery will automatically stringify your request data.
Change to:
$.ajax({
type: "POST",
url: hb_base_url + "consumer",
contentType: "application/json",
dataType: "json",
data: JSON.stringify({
first_name: $("#namec").val(),
last_name: $("#surnamec").val(),
email: $("#emailc").val(),
mobile: $("#numberc").val(),
password: $("#passwordc").val()
}),
success: function(response) {
console.log(response);
},
error: function(response) {
console.log(response);
}
});