Cannot build indeces in backoffice

I am trying to install Litium 8 and got to the step of building the indeces. The first time i got a bunch of errorrs and now the option to rebuild the indeces in the backoffice is disabled. What do I need to do?

Litium version: 8.8

Start with investigating the litium.log and elasticsearch.log. The error has to be logged in one of them.