I think that still classes as work and payments, albeit in kind.
I might be making this up but work is anything that a person would normally be expected to be paid for. So even volunteering in a charity shop is out as someone in a shop would usually be paid. Sure I’ve read that some where.... 🤔 might be to do with tourist visas....
There is already a solid agreement in place to allow Brits settled in Spain to stay, what a pity you weren’t advised of that.
I suggest reviewing that idea as even with Brexit, you will be better off in Spain.