Not fully understand your question, base on my assumption here is what I think
You want to handle the error/exception if any thrown from your API.
You can simply use the catchError operator from rxjs/operators and write something like this.
return this.http.get(this.partySiteAddressUrlOrganization + "?" + new Date().toString(), { params: newparams })
.pipe(
concatMap((result1: any) => {
return this.http.post(this.postRequestListURL, parm)
}),
catchError((error)=>{
// handle the error
// if you want to throw it the throw other wise send the EMPTY its up to you
// using return EMPTY;
}));
If first one is not your scenario and you are saying your API will return a flag if something is not right then you can handle this like
return this.http.get(this.partySiteAddressUrlOrganization + "?" + new Date().toString(), { params: newparams })
.pipe(
concatMap((result1: any) => {
if(result1.success) {
return this.http.post(this.postRequestListURL, parm)
} else {
// handle your stuff here and the return
return of({}); // {} can be your object
}
}),
catchError((error)=>{
// handle the error
// if you want to throw it the throw other wise send the EMPTY its up to you
}));