It sounds like acknowledging the sponsors is "the right thing", good Karma, or simply advertising for them. Not everyone wants to just rip off open source and not give back, they're willing to share the wealth if you make it easy and let people know they're doing it?
I need to set up github sponsors myself. We get the occasional request "how can I contribute money to you guys" and we always say stuff like "just spread the word". I keep telling myself I don't want to feel obligated by money, but I also know that I'd love to make enough to work on open source full time.
Also I can recommend OpenCollective; I’m sure there are other similar solutions as well. It’s nice to be able to “expense” stuff and I’m sure donors appreciate transparency.
What will help fix that issue is my wife going shopping with the kids long enough for me to figure what is wrong. ;)
I talked with the makers or manufacturer and we reached an agreement. So to me (and them) it's royalties.
It's not a contract, as the term "royalty" implies, but it is a royalty in the sense that it's determined per unit sold.