Relationship manager modal not opening

class ActivitiesRelationManager extends RelationManager
{
    protected static string $relationship = 'activities';

    protected static ?string $title = 'Activities';

    protected static ?string $recordTitleAttribute = 'name';

    protected static ?string $inverseRelationship = 'checklists';

    public function form(Form $form): Form
    {
        return $form
            ->schema([
                TextInput::make('name')
                    ->required()
                    ->maxLength(255),
                TextInput::make("description")
                    ->helperText("Do not enter credentials or sensitive information here."),
                TextInput::make("url")
                    ->label("URL"),
            ]);
    }

    public function table(Table $table): Table
    {
        ...
    }
}