The JSON Value Could Not Be Converted to System.Int32

What's causing JsonException: The JSON value could not be converted?

your Rootobject class would be working if your json starts with this

{ "property1": [{"id": 1148082,"name": .....] }

and the array had a property name. but your json don't have property1, so you should start to deserialize json array directly

Class1[] result = System.Text.Json.JsonSerializer.Deserialize<Class1[]>(json);

Angular 10 the JSON value could not be converted to System.Int32, asp.net

I have solved the question with changing some part of html.
Regarding the help with these answers;

Angular select value string parsing to integer

Changed html;

  <div class="td">
        <select class="form-control" formControlName="jobType">
          <option [ngValue]="0">Select</option>

          <option *ngFor="let item of toDoTypesArray" [ngValue]="item.typeId"> {{item.typeName}}</option>
        </select>
      </div>

Why it occurs this error [The JSON value could not be converted to System.Nullable] when ASP.NET Core is upgraded from 2.1 to 3.1?

I think you use the old jsonoption in ConfigureService. Since starting from ASP.NET Core 3.0, its default built-in JSON serialization and deserialization library is System.Text.Json. This library does not implement JSON conversion of these special data types like Json.NET. , so you can add nuget package newtonsoft to replace the built-in JSON serialization library System.Text.Json. And configure it in startup.

services.AddControllers().AddNewtonsoftJson();

The JSON value could not be converted to System.Nullable[System.Int32]

Here Via the json you pass a string value for UserId but your model refer a int32? value for UserId. Then how your value convert from string to int32?

Error The JSON value could not be converted to System.String. Path: $[1].Interests[1].Meta[9].Content | LineNumber: 0 | BytePositionInLine: 10073.

Can only use array initializer expressions to assign to array types. Try using a new expression instead.

You can convert the json data to Section type rather than List<Section> type.

var json = "{\"Booking\":\"\",\"Interests\":[{\"Title\":\"\",\"Meta\":[{\"Type\":\" \",\"Content\":\" \"}],\"Images\":[{\"content\":\" \",\"alt\":\" \"}]}]}";
            var s = JsonConvert.DeserializeObject<Section>(json);
            //If you want to set Employee.Sections with json data,try this
            Employee e = new Employee { Sections = new List<Section> { s } };

Models(change class name Sections to Section,Interests to Interest):

public class Employee
    {

        public string Name { get; set; }

        [Column(TypeName = "jsonb")]
        public List<Section> Sections { get; set; }

    }

    public class Section
    {

        public string Booking { get; set; }

        [Column(TypeName = "jsonb")]
        public List<Interest> Interests { get; set; }

    }

    public class Interest
    {

        public string Title { get; set; }

        public List<Meta> Meta { get; set; }

        public List<WithAlt> Images { get; set; }
    }

    public class Meta
    {

        public string Type { get; set; }

        public string Content { get; set; }

    }

    public class WithAlt
    {

        public string content { get; set; }

        public string Alt { get; set; }

    }

“The JSON value could not be converted to System.String” when attempting to call controller endpoint

The model binder is unable to map/bind the sent data to the controller parameters

Your action expects a simple string from the request body

public async Task<ActionResult> AddQuestion([FromBody] string question)

But you sent a complex object

{ "test" : "test" }

You might have gotten a match if the property name(s) had matched

For example

{ "question" : "test" }

Since the model binder will take property names into consideration when matching parameters.

if you want to receive a raw string then you need to send a valid raw JSON string

"{ \"test\": \"test \"}"

That is properly escaped.

Another options is to use a complex object for the parameter

class Question  {
    public string test { get; set; }
    //...other properties
}

that matches the expected data

public async Task<ActionResult> AddQuestion([FromBody] Question question) {
    string value = question.test;

    //...
}

The model binder will bind the data and pass it to the action parameter(s).

Reference Model Binding in ASP.NET Core

Posting in blazor returns exception stating that The JSON value could not be converted to System.Int32.

You are not returning an int (the Id). You're returning an anonymous object with an int property named Id.
Try

return Ok(createdId);