Plugin Support
Femi
(@femiyb)
Hello @ferhat1986
We have released a beta package that should resolve this issue. You can download the beta package here: https://github.com/mollie/WooCommerce/releases/tag/8.0.5-beta2
This fix will be included in the next release.
Please let me know if this works for you.
Regards,
Femi.
Hi Femy,
Thnx for the reply. We still get the same error:
2025-08-05T12:11:41+00:00 Debug [2025-08-05T12:11:41+0000] Error executing API call (422: Unprocessable Entity): Line item 1 is invalid. The 'vatAmount' field is off. Expected to be €137.09 (€789.89 × (21.00 / 121.00)), got €137.00. Documentation: https://docs.mollie.com/reference/handling-errors. Request body: {"status":422,"title":"Unprocessable Entity","detail":"Line item 1 is invalid. The 'vatAmount' field is off. Expected to be €137.09 (€789.89 × (21.00 / 121.00)), got €137.00","field":"lines.1.vatAmount","_links":{"documentation":{"href":"https://docs.mollie.com/reference/handling-errors","type":"text/html"}}}. Field: lines.1.vatAmount
2025-08-05T12:11:41+00:00 Debug ideal: Failed to create Mollie payment object for order 296295: [2025-08-05T12:11:41+0000] Error executing API call (422: Unprocessable Entity): Line item 1 is invalid. The 'vatAmount' field is off. Expected to be €137.09 (€789.89 × (21.00 / 121.00)), got €137.00. Documentation: https://docs.mollie.com/reference/handling-errors. Request body: {"status":422,"title":"Unprocessable Entity","detail":"Line item 1 is invalid. The 'vatAmount' field is off. Expected to be €137.09 (€789.89 × (21.00 / 121.00)), got €137.00","field":"lines.1.vatAmount","_links":{"documentation":{"href":"https://docs.mollie.com/reference/handling-errors","type":"text/html"}}}. Field: lines.1.vatAmount
Strange thing is that the VAT is also getting rounded. The product price should be 790 incl VAT
VAT should be 137,11 but also gets rounded to 137
Plugin Support
Femi
(@femiyb)
Hello @ferhat1986
Looked into this further. The problem occurs in the order lines processing system where WooCommerce displays products as €350 (rounded from €349.95) but Mollie expects precise VAT calculations based on the actual €349.95 price. OrderLines.php:159-163 The vatAmount field is calculated using WooCommerce’s internal tax amounts, which may not align with Mollie’s validation formula.
To resolve this without any custom code changes, we recommend updating your WooCommerce settings to preserve precision in your price calculations. Here’s how:
- Go to WooCommerce > Settings > General
- Scroll to Currency options
- Change “Number of decimals” from
0 to 2
This change ensures that the full product prices (e.g., €349.95) are used throughout the calculation process and sent to Mollie, which should prevent the VAT mismatch errors you’re encountering.
Please let me know if this works.
Regards,
Femi.
Hi Femi,
This option is what is causing the problem. We purposely set the decimals to 0. We don’t want to show decimals in our webshop.
Isn’t there a way to make the plugin work with decimals set to 0?
Greetings,
Ferhat
Some extra information
I have set the decimals to 0
I have a product which is priced on 350,00 exactly including 21% taxes
So the price is as following:
Product price excluding taxes (21%): €289,26
Tax (21%): €60,74
Product price including taxes (21%): €350
When trying to pay this order (€350 incl €61 taxes) the error log says the same:
2025-08-13T08:43:44+00:00 Foutopsporing {
"amount": {
"currency": "EUR",
"value": "350.00"
},
"description": "Bestelling ",
"redirectUrl": "https://xxxx.com/betalen/order-received/xxxx/?key=xxxx&order_id=xxxx&filter_flag=onMollieReturn",
"webhookUrl": "https://xxxx.com/wc-api/mollie_wc_gateway_ideal?order_id=xxxx&key=xxxx&filter_flag",
"method": "ideal",
"issuer": "",
"locale": "nl_NL",
"dueDate": "",
"metadata": {
"order_id": xxxx
}
}
2025-08-13T08:43:45+00:00 Foutopsporing [2025-08-13T08:43:45+0000] Error executing API call (422: Unprocessable Entity): Line item 1 is invalid. The 'vatAmount' field is off. Expected to be €60.79 (€350.26 × (21.00 / 121.00)), got €61.00. Documentation: https://docs.mollie.com/reference/handling-errors. Request body: {"status":422,"title":"Unprocessable Entity","detail":"Line item 1 is invalid. The 'vatAmount' field is off. Expected to be €60.79 (€350.26 × (21.00 / 121.00)), got €61.00","field":"lines.1.vatAmount","_links":{"documentation":{"href":"https://docs.mollie.com/reference/handling-errors","type":"text/html"}}}. Field: lines.1.vatAmount
2025-08-13T08:43:45+00:00 Foutopsporing ideal: Failed to create Mollie payment object for order xxxx: [2025-08-13T08:43:45+0000] Error executing API call (422: Unprocessable Entity): Line item 1 is invalid. The 'vatAmount' field is off. Expected to be €60.79 (€350.26 × (21.00 / 121.00)), got €61.00. Documentation: https://docs.mollie.com/reference/handling-errors. Request body: {"status":422,"title":"Unprocessable Entity","detail":"Line item 1 is invalid. The 'vatAmount' field is off. Expected to be €60.79 (€350.26 × (21.00 / 121.00)), got €61.00","field":"lines.1.vatAmount","_links":{"documentation":{"href":"https://docs.mollie.com/reference/handling-errors","type":"text/html"}}}. Field: lines.1.vatAmount
As you can see, somehow €350 gets converted to €350,26. I’ve repeated this step in a clean WordPress and WooCommerce environment and got the same problem.
It seems like there is a bigger issue with setting the decimals to 0 in WooCommerce and the problem isn’t really in the Mollie plugin but rather in the way WooCommerce handles decimals with this setting.
Instead of using the WooCommerce setting “Number of decimals” and setting it to 0, i used a WooCommerce filter to trim the zeros:
add_filter( 'woocommerce_price_trim_zeros', '__return_true' );
This way the user will only see decimals in VAT, shipping costs and at the total order price. In my case “Cart” & “Checkout” pages.
