Could not Create Label -Login failed

Hi there,
I’m currently experiencing the following problem. After I marked the order as completed in the system, it should be possible to just click on the “create label” button of DHL plugin (Version 2.7.1.) and receive the shipping label as a downloadable file. Unfortunatley, this doesn’t happen and an error message is shown: “could not create label, login failed”. I figured this is a problem of me maybe accidentally having entered faulty data in the settings of the plugin, so I double checked but this was not the case. I am also able to login to DHL Business Portal. I also checked with DHL support to make sure it’s not an issue with my account but the confimed it isn’t and I should ask WooCommerce Support.
What could be the solution to this problem?