Hi,
Yes, there are differences between the 2. The main differences are that the plugin will connect to another server, and the available shipping carriers are not the same for each country.
We actually did a new version of the MyParcel plugin 2 months ago to support MyParcel.be as it only supported MyParcel.nl before that.
We did test the plugin with a MyParcel.be account, but maybe you found some bug.
Could you first provide a screenshot of the settings you have for the MyParcel plugin via the Joomla plugins manager ?
And could you also provide a screenshot of the order details with the address, the products etc of the order you're using for your test ?
If you want, you can go through our contact form to provide these confidentially:
www.hikashop.com/support/contact-us.html
Even better whole be a backend access so that we could check the situation.