mat-select Not Working Properly

The message says that your select must be in a mat-form-field, not in the same mat-form-field as your input. Try this:

<mat-form-field>
    <input matInput placeholder="Name" #NameInput>
</mat-form-field>

<mat-form-field>
    <mat-select placeholder="How Many?">
        <mat-option>One</mat-option>
        <mat-option>Two</mat-option>
        <mat-option>Three</mat-option>
        <mat-option>Four</mat-option>
        <mat-option>Five</mat-option>
    </mat-select>
</mat-form-field>

In the doc that's how they do: https://material.angular.io/components/form-field/overview

Silly me, I forgot to import MatSelectModule in my app.module.ts.

I mistakenly put placeHolder [in camelCase] instead of placeholder and it just ignored this!!!

It was very hard to find! but once I changed to placeholder I was able to see it. Just wanted to share in case you may also have run into..