Add a checkbox to export the donation Transaction ID in GiveWP donation history export

give_export_transaction_id.php

<?php

function give_export_transaction_id() {
	?>
	<tr class="give-export-option-fields give-export-option-custom-field">
				<td scope="row" class="row-title">
					<label><?php esc_html_e( 'Transaction ID:', 'give' ); ?></label>
				</td>
				<td class="give-field-wrap">
					<div class="give-clearfix">
						<ul class="give-export-option-custom-fields-ul">
							<!-- Custom field checkbox -->
							<li class="give-export-option-start">
								<label for="give-custom-field">
									<input type="checkbox" checked
									       name="give_give_donations_export_option[transaction_id]"
									       id="give-export-transaction_id"><?php _e( 'Transaction ID', 'give' ); ?>
								</label>
							</li>
						</ul>
					</div>
				</td>
			</tr>
	<?php
}

add_action( 'give_export_donation_fields', 'give_export_transaction_id' );

/**
* Thi function sets the column header in the generated CSV file for the custom field. Add an if statement for each aditional field.
*/
function give_export_transaction_id_column_header( $cols ) {
	if ( isset( $cols['transaction_id'] ) ) {
		$cols['transaction_id'] = __( 'Transaction ID', 'give' );
	}

	return $cols;

}

add_filter( 'give_export_donation_get_columns_name', 'give_export_transaction_id_column_header' );

/**
* This function populates the CSV with the custom field data. Add an if statement for each aditional field.
*/
function give_export_transaction_id_data( $data, $payment, $columns ) {
	if ( ! empty( $columns['transaction_id'] ) ) {
		$transactionID = $payment->get_meta( '_give_payment_transaction_id' );
		$data['transaction_id'] = isset( $transactionID ) ? wp_kses_post( $transactionID ) : '';
	}

	return $data;
}

add_filter( 'give_export_donation_data', 'give_export_transaction_id_data', 10, 3 );