Laravel: Soft Delete does not populate "deleted_at" column; regular delete works

Tearing my hair out over this one... Cannot get soft deleting to work in Laravel 5.x.

The "deleted_at" column is never populated with the timestamp.

If I remove "use SoftDeletes" from the model, it deletes the item (as expected), but soft deleting does nothing.

Here is my code:

Model:

class UkRfpEntry extends Model
{

use SoftDeletes;

    /**
     * The attributes that should be mutated to dates.
     *
     * @var array
     */
protected $dates = ['deleted_at'] ;   

public function metadata()
    {
        return $this->hasOne('App\UkRfpEntryMetadata');
    } 


}

Contoller:

 public function destroy(UkRfpEntry $uk_rfp_entry)
    {

        $uk_rfp_entry->delete();    

    }

(successful) Migration:

public function up()
    {
        Schema::table('uk_rfp_entries', function (Blueprint $table) {
             $table->softDeletes();
        });
    }

AJAX request for deletion:

$.ajax({

    url: "" + "/" + $(this).attr('id'), // the url where we want to POST
    type: 'DELETE',
    data:  {
            '_token': '',
            '_method': 'DELETE',           

        },
    dataType: 'json',    
    success: alert('success')

    });

via Chebli Mohamed