[solved] error NG8002: Can't bind to 'formGroup' since it isn't a known property of 'form'.

Solution

You just need to import ReactiveFormsModule from @angular/forms in your module. Here's the example of a basic module with ReactiveFormsModule import:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { AppComponent }  from './app.component';

@NgModule({
    imports: [
        BrowserModule,
        FormsModule,
        ReactiveFormsModule
    ],
    declarations: [
        AppComponent
    ],
    bootstrap: [AppComponent]
})

export class AppModule { }

Warning 

If you use Ionic modals, also import it to the parent (f.e. the pageComponent) where you render your modal in!