PaySlate vs Flexible Invoices
Flexible Invoices is the largest genuinely standalone invoicing plugin in the WordPress directory, at around 6,000 active installs, and it is actively maintained. We build PaySlate, so the bias is disclosed up front, and the places Flexible Invoices genuinely beats us are stated plainly below. Every claim here was verified in August 2026.
The difference is one of purpose. Flexible Invoices is fundamentally a document generator: it produces compliant PDF invoices, both for WooCommerce orders and standalone, with particularly strong support for Polish and EU e-invoicing requirements including KSeF. PaySlate is a get-paid tool: the invoice is a page your client opens and pays on, and the plugin’s job is finished when the money arrives.
At a glance
| PaySlate | Flexible Invoices | |
|---|---|---|
| Core job | Send an invoice and collect payment | Generate a compliant invoice document |
| Card payment on the invoice | Yes, Stripe and Square free | Not its purpose |
| Deposits and partial payments | Yes, balance tracked | No |
| Automatic overdue reminders | Yes | No |
| Polish KSeF and EU e-invoicing formats | No | Yes |
| WooCommerce order invoices | Coexists with WooCommerce | Yes, a core strength |
| Merchant of record for VAT and sales tax | Yes, on Pro | No |
| Active installs | New (launched July 2026) | ~6,000 |
Compliance versus collection
If you are invoicing in Poland, or anywhere the tax authority dictates the invoice format, Flexible Invoices is solving a problem PaySlate does not touch. Structured e-invoicing formats are not a nice-to-have in those markets, they are the law, and a plugin built around them is the right tool.
PaySlate approaches tax from the opposite end. Rather than formatting a document to satisfy a filing requirement, Pro lets you route payment through Paddle or Lemon Squeezy so that a merchant of record becomes the seller and handles registration and remittance. Different problem, different answer.
What happens after you send it
A PDF is a file. Someone still has to open it, read the bank details, make a transfer, and tell you they did. Then you reconcile it by hand.
A PaySlate invoice is a page on your domain with a pay button. Your client pays by card, Apple Pay or Google Pay, the invoice flips to paid by webhook, and the receipt sends itself. If it goes past its due date, the reminder goes out without you writing it. That is the entire difference in a sentence: one produces a document, the other closes the loop.
Where Flexible Invoices wins
Regulatory formats. KSeF and EU structured e-invoicing. If you need these, this comparison is already over.
WooCommerce order invoicing. If your job is attaching a proper invoice PDF to orders a store already took, that is squarely its territory and not PaySlate’s.
Track record. Around 6,000 installs and regular releases, against a plugin launched in July 2026.
Which one fits you
Choose Flexible Invoices if the invoice is a compliance document, or if it belongs to a WooCommerce order.
Choose PaySlate if the invoice is how you get paid, and you want the payment, the status and the reminders handled on your own site. See what PaySlate does or pricing.