Once I select an item from the Category dropdown list and hit save button, I am getting an error msg as follows:

The JSON value could not be converted to System.Collections.Generic.List`1[System.Guid]. Path: $.categories | LineNumber: 0 | BytePositionInLine: 377

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I want to select just single item from the category dropdown list. It looks like there is an issue when I assign value from the selected list.

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categories: this.selectedCategories ?? []

my edit-tentry.component.html looks like this

<ng-container *ngIf="categories$ | async as categories">
    <select class="form-control" [(ngModel)]="selectedCategories" name="categories">
        <option *ngFor="let category of categories;" [value]="category.id">{{category.name}}    
        </option>                            
    </select>                        
</ng-container>

my edit-tentry.component.ts looks like

export class EditTentryComponent implements OnInit, OnDestroy {

  id: string | null = null;
  model?: Tentry  
  categories$?: Observable<Category[]>;
  selectedCategories?: string[];

  ngOnInit(): void {

    this.categories$ = this.categoryService.getAllCategories();

    this.routeSubscription = this.route.paramMap.subscribe({
      next: (params) => {
        this.id = params.get('id');

        //Get Tentry from API
        if(this.id){
          this.getTentrySubscription = this.tentryService.getTentryById(this.id).subscribe({
            next: (response) => {
              this.model = response;
              this.selectedCategories = response.categories.map(x => x.id); 
            }
          });
        }

        console.log("Get Selected Categories On InIt: ", this.selectedCategories);
       
      }
    });    
  }

    onFormSubmit(): void{      
    
      if(this.model && this.id)
      {
        var updateTentry: UpdateTentry = {
          //......
          //......
          ticketStatus: this.model.ticketStatus,
          categories: this.selectedCategories ?? []
        
      };
     

       this.updateTentrySubscription = this.tentryService.updateTentry(this.id, updateTentry) 
       .subscribe({
        next:(response) => {
          this.router.navigateByUrl('/admin/tentry')
        }
       });
     }
   }

 export interface Category {
    id: string;
    name: string;
    urlHandle: string;
  }