Plugin version 1.3.6 finally solves this bug.
The fatal error occurs when we update the ActiveCampaign for Woocommerce plugin to version 1.2.12 or 1.2.13. Version 1.2.11 works fine. Thanks in advance!
Same error at our end! Our PHP version is 7.4.11.
Beste @postnl support,
Dank! Ik zal het doorgeven aan onze fulfilmentpartij.