Sliced Invoices: use same terms and conditions from Quote on the Invoice when converting a Quote to Invoice, or creating a new Invoice from an existing Quote

functions.php

function si20220524_preserve_quote_terms_on_invoice_before( $id ) {
	global $si20220524_quote_terms;
	$si20220524_quote_terms = get_post_meta( $id, '_sliced_quote_terms', true );
}
function si20220524_preserve_quote_terms_on_invoice_after( $id, $new_post_id = null ) {
	global $si20220524_quote_terms;
	if ( $si20220524_quote_terms ) {
		if ( $new_post_id ) {
			// created new invoice from quote
			update_post_meta( $new_post_id, '_sliced_invoice_terms', $si20220524_quote_terms );
		} else {
			// converted quote to invoice
			update_post_meta( $id, '_sliced_invoice_terms', $si20220524_quote_terms );
		}
		$si20220524_quote_terms = null;
	}
}

// for admin "convert quote to invoice" button:
add_action( 'sliced_invoices_admin_before_convert_quote_to_invoice', 'si20220524_preserve_quote_terms_on_invoice_before' );
add_action( 'sliced_invoices_admin_after_convert_quote_to_invoice', 'si20220524_preserve_quote_terms_on_invoice_after' );

// for admin "create new invoice from quote" button:
add_action( 'sliced_invoices_admin_before_create_invoice_from_quote', 'si20220524_preserve_quote_terms_on_invoice_before' );
add_action( 'sliced_invoices_admin_after_create_invoice_from_quote', 'si20220524_preserve_quote_terms_on_invoice_after', 10, 2 );

// for frontend "accept quote" button:
add_action( 'sliced_invoices_client_before_accept_quote', 'si20220524_preserve_quote_terms_on_invoice_before' );
add_action( 'sliced_client_accepted_quote', 'si20220524_preserve_quote_terms_on_invoice_after', 10, 2 );