What occurs if a payment is overdue, depends on what the invoice was for:
Site Maintenance - there will be no updates to your site until we receive payment.
Hosting - your site will be temporarily offline. If payment is received within 7 business days, it will reactivate. After that we will assume the account is closed, and there will be an additional $25 fee to reactivate the account and re-install the files. (If you manage your own web site, it is up to you to reinstall the files - UltiHost will keep site files that we mange for 90 days, then they are deleted and a new site will have to be designed, with all fees incured.)
Site Design - payment in full is required for us to release the site files to the client, or to install them online.
All other billable add-on or custom items are paid in full in advance.