Erro Generate Export

hi,
I’m trying to export, but this one has this error. what should I do?

membership2 -> import tool -> Export data

Fatal error: Class ‘MS_Addon_Coupon_Model’ not found in /home/mysite/public_html/wp-content/plugins/membership/app/model/import/class-ms-model-import-export.php on line 193

in file –> class-ms-model-import-export.php

188 // Export plugin settings.
189 $obj = array();
190 $data->settings = $this->export_settings();
191
192 // Export Coupons.
193 $coupons = MS_Addon_Coupon_Model::get_coupons( array( ‘nopaging’ => true ) );
194 $data->coupons = array();
195 foreach ( $coupons as $coupon ) {
196 if ( intval( $coupon->max_uses ) <= intval( $coupon->used ) ) { continue; }
197 $data->coupons[] = $this->export_coupon( $coupon->id );
198 }
199
200 lib3()->net->file_download( json_encode( $data ), ‘membership2-export.json’ );
201 }

Thanks