Unable to load a world with data packs

It is possible to create a map without datapack and get to connect me but as soon as I try to add datapacks, the map is created but it is impossible to connect to it. 

After a very long loading time, an error message is displayed: 

"An error occurred, please try again later"

I hope you can help me to solve this problem because I do not really want to have paid a realm for nothing...

Thank you in advance.