Thank you for reaching out to us. We’re sorry that you’re experiencing an issue.
Unfortunately, a plugin CheckoutWC and GLS Shipping have not been tested for compatibility with each other, and therefore we can’t guarantee that they work together.
We have added this compatibility issue to our backlog and we would like to release an update with a fix at some point.
If you can’t use a different way of building the check-out page, with compatibility issues like that, you can request individual support, where we could help you with your particular case. This is a paid service as it requires extensive use of our time.