Shamim's Plugins

Users can see groups in dropdown which they are member.
May be i did not understand you properly. can not user see all groups which they are member in dropdown?

Add following code in your theme’s (child theme’s if you are using) functions.php

add_filter( 'fep_form_fields', function( $fields ){
	$fields['cus_fep_checkbox'] = [
		'type'     => 'checkbox',
		'where'    => 'newmessage',
		'priority' => 22,
		'cb_label' => 'Can we use your message on the site as a story?',
	];
	return $fields;
});

add_action( 'fep_action_message_after_send', function( $message_id, $message, $new_message ){
	if ( ! empty( $message['cus_fep_checkbox'] ) ) {
		fep_add_meta( $message_id, 'cus_fep_checkbox', $message['cus_fep_checkbox'], true );
	}
}, 10, 3);

add_action( 'fep_display_after_message', function(){
	if ( fep_get_meta( fep_get_the_id(), 'cus_fep_checkbox', true ) ) {
		echo 'We can use this message on the site as a story';
	}
});

You can use fep_form_fields filter hook to add any additional fields and fep_display_after_message hook to show that bellow message.

You can add following code in your theme’s (child theme’s if you are using) functions.php

add_filter( 'wp_default_editor', function( $r ){
	return 'tinymce';
});

remember if user change tab (visual/text) then that will be saved and will use that instead.

User will get this error when reply if
1. Any recipient of that message deleted that message
2. Any user block current user

Please check these two condition.

If you have styling issue then remove previous code and add

onClick="window.location.href='<?php echo fep_query_url( 'viewmessage', [
	'fep_id' => fep_get_the_id(),
	'feppage' => isset( $_GET['feppage'] ) ? $_GET['feppage'] : 1,
	'fep-filter' => isset( $_GET['fep-filter'] ) ? $_GET['fep-filter'] : '',
] ); ?>'"

in that div. Also style that div to show cursor as pointer.

Thank you very much. Much appreciated.
I have sent you my paypal email in your email address.