Can't assign requested address (code=49) is a bug in macOS and not an issue with OVPN itself.
There are two ways of fixing this issue. The first one is easier as you simply have to restart your computer. Otherwise, you can solve the problem through the terminal. If you have a cable connection, you type the following into a terminal:
sudo ifconfig en0 down
sudo route flush
sudo ifconfig en0 up
If you instead use WiFi, you type:
sudo ifconfig en1 down
sudo route flush
sudo ifconfig en1 up
Type every line separately. If asked for your password, simply type the password for your computer and not for OVPN.
If the command sudo route flush takes longer than 10 seconds to complete, hold down Ctrl + C.