To create GLS Unibox as a carrier, you will need the following:
You get these from GLS, most likely in your e-mail inbox. However, you can always find them on your GLS Profile, or by contacting them.
To create the carrier, you will have to do the following:
Navigate to Webshipper and then Settings > Carriers > GLS Unibox
From here, you insert the information you have received from GLS.
Congratulations! You have now created GLS Unibox as a carrier, and you are now ready to use their services!