This happens when a form does not have required data in a ModalFormData, ActionFormData or MessageFormData class.
To solve this, you need to have required setting included in your script.
const ModalForm = new ModalFormData();
// Required
ModalForm.title(titleText: string);
// One of the following are needed: Dropdown / Slider / Textfield / toggle
ModalForm.dropdown(label: string, options: string[], defaultValueIndex?: number);
ModalForm.slider(label: string, minimumValue: number, maximumValue: number, valueStep: number, defaultValue?: number);
ModalForm.textField(label: string, placeholderText: string, defaultValue?: string);
ModalForm.toggle(label: string, defaultValue?: boolean);
// Show form to player
ModalForm.show(player: Player);
Example:
new ModalFormData().title('ModalFormData')
.dropdown('Dropdown', ['Option 1', 'Option 2'])
.show(player)
const form = new MessageFormData();
// required
form.title('Title');
form.body('Body');
// optional
form.button1('button1');
form.button2('button2');
// Show form to player
ModalForm.show(player);
import { ActionFormData } from '@minecraft/server-ui';
const action = new ActionFormData();
// required
action.title('title');
action.body('body');
// require at least one button
action.button('button');
// show
action.show(player);