Invoicing in WHMCS with Moloni ON

Running a web hosting, subscription, or digital services business with WHMCS can dramatically simplify your day-to-day operations. However, when it comes to issuing invoices that fully comply with Portuguese tax legislation, things become more complex. This is where integrating with an invoicing solution certified by the Portuguese Tax and Customs Authority (AT) makes all the difference. In this article, we'll explain how connecting your WHMCS platform to Moloni ON can automate your invoicing workflow, ensure full legal compliance, and provide a seamless experience for both you and your customers.

Key takeaways

• Complete automation: Automatically converts WHMCS billing cycles and payment orders into certified invoices in Moloni ON.
• Full tax compliance: Ensures invoices are digitally signed and communicated to the Portuguese Tax Authority in real time or through the monthly SAF-T (PT) submission.
• Data synchronisation: Instantly synchronises customers, products, VAT rates, and tax exemptions between both platforms.
• Fewer manual errors: Eliminates duplicate data entry, reducing accounting mistakes and saving hours of administrative work.

What is the WHMCS plugin for Moloni ON?

The WHMCS plugin for Moloni ON acts as a bridge between your customer management platform (CRM) and your certified invoicing system. When you run an online store or subscription-based business using WHMCS, the platform automatically generates invoices or payment requests. However, if you operate in Portugal, the final fiscal document must be issued through software certified by the Portuguese Tax Authority.

Once the plugin is installed, the process becomes fully automatic. As soon as a customer pays an invoice in WHMCS, the billing information is immediately sent through the Moloni ON API. Moloni ON then generates the official certified invoice, creates the PDF document, and, depending on your configuration, either attaches it to the customer's WHMCS account or sends it directly by email.

How does the automatic invoicing process work?

The integration has been designed to work silently in the background, removing manual intervention from your billing routine while creating a smoother customer experience.

From order to certified invoice

The process starts when a customer purchases a hosting plan, renews a domain, or subscribes to one of your services through WHMCS. The platform creates an internal invoice that serves as a payment request. Once the payment gateway confirms the transaction, WHMCS marks the invoice as Paid.

This status change triggers the plugin automatically. It collects the customer's name, Tax Identification Number (NIF), address, purchased items, and corresponding values before securely transmitting the information to Moloni ON via an encrypted API connection.

Invoice generation and delivery

Moloni ON receives the information, validates the customer's fiscal details, and issues the appropriate document—typically an Invoice or Invoice-Receipt. The software automatically applies the correct VAT rules, generates the certified document, and returns both the invoice number and the PDF link to WHMCS. Within seconds, your customer receives the official invoice without any manual intervention.

What are the tax advantages of using Moloni ON with WHMCS?

Operating in Portugal requires strict compliance with the rules established by the Portuguese Tax and Customs Authority (AT). Since WHMCS is an international platform, it isn't built to support Portuguese-specific requirements such as SAF-T (PT) reporting or reverse charge VAT rules. Using Moloni ON ensures complete legal compliance.

Certified invoicing

Moloni ON is fully certified by the Portuguese Tax Authority, meaning every invoice includes the legally required digital signature and follows the mandatory sequential numbering system.

Automatic SAF-T (PT) reporting

Whether you report your invoices monthly or in real time, Moloni ON centralises all billing information generated through WHMCS. This allows you to generate the SAF-T (PT) file directly from Moloni ON or enable automatic communication with the Tax Authority, removing the need to combine reports from multiple systems.

How do you configure VAT rates and exemptions correctly?

Managing VAT correctly is one of the biggest challenges when integrating international platforms with Portuguese tax software. Your VAT configuration in WHMCS should match the tax settings configured in Moloni ON.

If you sell services internationally, you'll also need to account for EU reverse charge rules and VAT exemptions for customers outside the European Union. The integration maps these rules automatically. For example, when WHMCS identifies a customer with a valid EU VAT number through VIES, Moloni ON applies the appropriate legal VAT exemption under the relevant Portuguese VAT Code articles.

If you sell to consumers (B2C) within the European Union and are registered under the One Stop Shop (OSS) scheme, Moloni ON can automatically apply the destination country's VAT rate, keeping your accounting compliant and audit-ready.

Which documents can be issued automatically?

Depending on your business model, you can configure the integration to generate different document types automatically.

• Invoice-Receipt: Ideal for businesses where payment is immediate, such as credit card transactions or automated Multibanco payments. The document is issued already marked as paid.
• Invoice: Suitable when customers are given payment terms. The invoice is issued as outstanding, and once payment is received, Moloni ON generates the corresponding receipt automatically.
• Credit Note: Perfect for automating refunds and cancellations. If an order is refunded or cancelled in WHMCS, the integration can automatically instruct Moloni ON to issue a Credit Note, reversing or correcting the original invoice.

What happens if a customer updates their billing information?

Customers frequently update their address, company name, or Tax Identification Number (NIF) through the WHMCS client area. A properly configured integration ensures your invoicing records remain accurate.

Whenever a new invoice is generated, the plugin checks whether the customer already exists in Moloni ON using the NIF or another unique identifier. If any information has changed, the customer profile is updated automatically before the new fiscal document is created. This prevents duplicate customer records while ensuring your customer database and SAF-T (PT) file always contain accurate and up-to-date information.