

You could add a word or phrase to remind people that it’s being given away for free to anyone that wants to run it. That might get people to think about any benefit they are getting out of it, and how much they want to donate in response.
I’m not sure what is the best wording for that, but just be careful in case someone misunderstands and thinks it might become paid someday. I’ve seen that complaint in the past
For example, this could be misinterpreted:
and if you want to keep using it for free
You can also add a note about the frequency of the messages. Saying that you will only remind people once a year is nice to hear, and that way people won’t dismiss it thinking they will do it when they are reminded the next time
Nice, I like it :)