Get selection and save as shipping meta data

betrs-save-custom-meta.php

/**
 * Find the custom column selection when calculating shipping
 *
 * @return string
 */
function betrs_add_custom_data_shipping_array( $shipping_options, $option, $option_ID, $row_ID ) {

    // find selected value from table
    $selection = ( isset( $option['rows'][ $row_ID ]['provider'] ) ) ? sanitize_text_field( $option['rows'][ $row_ID ]['provider'] ) : '';

    // add to shipping option
    if( $selection != '' ) {
        $shipping_options['provider'] = $selection;
    }

    return $shipping_options;
}
add_filter( 'betrs_processed_rate', 'betrs_add_custom_data_shipping_array', 10, 4 );

/**
 * Add provider to meta data if selected.
 *
 * @return void
 */
function betrs_modify_shipping_rate_meta( $meta_data, $rate ) {
    // check if the provider has been selected
    if( ! empty( $rate['provider'] ) ) {
        $meta_data['provider'] = sanitize_text_field( $rate['provider'] );
    }

    return $meta_data;
}
add_filter( 'betrs_shipping_rate_meta', 'betrs_modify_shipping_rate_meta', 10, 2 );