Two slashes in webhook logs

Hi

I have successfully installed and integrated zahls.ch while using TWINT and credit cards.

However, when performing a TWINT transaction via webshop, the webhook fails and contains an URL like this:
… //?wc-api=wc_payrexx_gateway

Why does it have two slashes at the beginning?

zahls v.2.0.4
WooCommerce 9.4.1

Thanks a lot
Michael