Sisow Payment methods for WooCommerce 1.6 and WooCommerce 2.X
You didn't enter a MerchantID in the configuration
You didn't enter a MerchantKey in the configuration
The order total is lower than 0.45
You didn't choose a payment method in the checkout
Error on your server, check or CURL is enabled. If it is installed reboot your server.
A general error, please send the TA code to email@example.com
Enable the Test Mode in you Sisow Account under "Mijn Profiel" tab "Geavanceerd". Enable the first checkbox "Testen met behulp van simulator (toestaan)".
Send an e-mail to firstname.lastname@example.org with the given TA code.
Contact WP-engine, this is an cache setting at their side, the returnURL may not be cached.