engaged in as a pastime
"an amateur painter"
"gained valuable experience in amateur theatricals"
"recreational golfers"
"reading matter that is both recreational and mentally stimulating"
"unpaid extras in the documentary"
Not paid for.
"The unpaid volunteer worked at the shelter every weekend without receiving a salary."
The word unpaid is formed by adding the prefix un- to the past participle of pay. It entered English simply as a straightforward negation of having received payment.