functions.php

<?php

// Add fields to new vendor form
add_action( 'shop_vendor_add_form_fields', 'custom_add_vendor_fields', 2, 1 );
function custom_add_vendor_fields( $taxonomy ) {
	?>
	<div class="form-field">
		<label for="vendor_website"><?php _e( 'Vendor website' ); ?></label>
		<input type="text" name="vendor_data[website]" id="vendor_website" class="vendor_fields" /><br/>
		<span class="description"><?php _e( 'The vendor\'s website.' ); ?></span>
	</div>
	<?php
}

// Add fields to vendor edit form for admins to edit
add_action( 'shop_vendor_edit_form_fields', 'custom_edit_vendor_fields', 2, 1 );
function edit_vendor_fields( $vendor ) {

    $vendor_id = $vendor->term_id;
    $vendor_data = get_option( 'shop_vendor_' . $vendor_id );
    
    $vendor_website = '';
    if( isset( $vendor_data['website'] ) && ( strlen( $vendor_data['website'] ) > 0 || $vendor_data['website'] != '' ) ) {
        $vendor_website = $vendor_data['website'];
    }
    ?>
    <tr class="form-field">
        <th scope="row" valign="top"><label for="vendor_website"><?php _e( 'Vendor website' ); ?></label></th>
        <td>
            <input type="text" name="vendor_data[website]" id="vendor_website" class="vendor_fields" /><br/>
            <span class="description"><?php _e( 'The vendor\'s website' ); ?></span>
        </td>
    </tr>
    <?php
}

// Add fields to vendor details form for vendors to edit
add_action( 'product_vendors_details_fields', 'custom_vendor_details_fields', 10, 1 );
function custom_vendor_details_fields( $vendor_id ) {
    
    $vendor = get_user_vendor();
    $vendor_data = get_option( 'shop_vendor_' . $vendor->ID );
    $vendor_info = get_vendor( $vendor->ID );
    
    $vendor_website = '';
    if( isset( $vendor_data['website'] ) && ( strlen( $vendor_data['website'] ) > 0 || $vendor_data['website'] != '' ) ) {
        $vendor_website = $vendor_data['website'];
    }
    
    $html = '<p class="form-field">
                <label for="vendor_website">' . __( 'Website' ) . ':</label>
                <input type="text" name="wc_product_vendors_website_' . $vendor->ID . '" id="vendor_website" class="vendor_fields" />
             </p>';
    
    echo $html;
}

// Save fields from vendor details form
add_action( 'product_vendors_details_fields_save', 'custom_vendor_details_fields_save', 10, 2 );
function custom_vendor_details_fields_save( $vendor_id, $posted ) {
    
    $vendor_data = get_option( 'shop_vendor_' . $vendor_id );
    
    if( isset( $posted[ 'wc_product_vendors_website_' . $vendor_id ] ) ) {
        $vendor_data['website'] = $posted[ 'wc_product_vendors_website_' . $vendor_id ];
    }
    
    update_option( 'shop_vendor_' . $vendor_id, $vendor_data );
}

?>