Sketch Up License

I do use sketch up for multiple years. I just installed the latest version of Sketch Up (2019) but it does not except my license number. What could be the reason and what can i do to solve this issue?

Each SketchUp version has it’s own license. If you are trying to enter an old license, of course it won’t work. You need to have purchased a current license for SU2019.

With what character does the serial start?