Both Homerun products - HR and ATS - are billed together in one plan which is managed via your Homerun ATS account.
To access your invoices, simply login to your Homerun ATS account and head to Settings > Billing > Invoices.
All invoices will be available to download directly from this page.
Note: Card payments are processed quickly, and so invoices will also appear almost instantly. However, please be aware that if you pay by SEPA Debit, your invoice will not appear until the payment has fully cleared and this can take a number of days.