Keep getting a message on empty price

I was looking for a plugin for an open price, but then I saw that the plugin that I use already has it build in. Booster is so nice!

But, I have not managed to get it working.

The ‘Message on Empty Price’ keeps popping up.
These are the settings I made on the product.

Setting: https://tppr.me/W6C1d

Hope you can help me, because I am very eager to launch this new product with this pricing strategy.

The page I need help with: [log in to see the link]