php - Angular 13 HttpParams strange behavior

one text

this is waht i get when i set params as intended by angular documentation. But to be honest i tried everything found in google with the same result. Why HttpParams methods not generating a normal json?

HttpParams {updates: Array(4), cloneFrom: HttpParams, encoder: HttpUrlEncodingCodec, map: null}
cloneFrom: HttpParams {updates: null, cloneFrom: null, encoder: HttpUrlEncodingCodec, map: null}
encoder: HttpUrlEncodingCodec {}
map: null
updates: Array(4)
0: {param: 'personalnummer', value: '3', op: 's'}
1: {param: 'vorname', value: 'fdsfds', op: 's'}
2: {param: 'name', value: 'fsdfsd', op: 's'}
3: {param: 'gruppe', value: '2', op: 's'}
length: 4
[[Prototype]]: Array(0)
[[Prototype]]: Object

Using params.keys on this gives me:

?� keys() {
    this.init();
    return Array.from(this.map.keys());
  }

No error message just a strange "whatever" but not a well formated json.

I tried params.set and params.append with completly the same result + the server says NULL for the incomming parameter, but doing ?variable=1 the server is acting as usually and reads perfectly the incomming data.

thx

EDIT:

getGruppe(gruppenbezeichnung:string):Observable<Benutzer[]>{
    const headers=new HttpHeaders()
    .set('Content-Type','application/json');

here is the problem
    const params=new HttpParams()
    .set ('gruppe',gruppenbezeichnung)



    return this.http.get<Benutzer[]>('einsatzplanBackend/getGruppe.php',{params:params,responseType:'json'}).pipe(
      catchError(this.handleError)
    )
  }

This is my solution and for Json objects i would use stringify but i would like to use the httpparam methods for paramter generation.

getGruppe(gruppenbezeichnung:string):Observable<Benutzer[]>{
    const headers=new HttpHeaders()
    .set('Content-Type','application/json');
    
    return this.http.get<Benutzer[]>('einsatzplanBackend/getGruppe.php?gruppe='+gruppenbezeichnung,{responseType:'json'}).pipe(
      catchError(this.handleError)
    )
  }