It's the future.Technology has progressed to the point where the vast majority of jobs can be done cheaper (and often more effectively) my autonomous machines than people. Most people are unemployed. They live reasonably comfortable lives on welfare, but it's still the bare minimum of what society considers "enough." Virtually all the wealth and power are concentrated in a small class of super-rich individuals.
Chattel slavery is still illegal, but people can sign "service contracts" that amount to almost the same thing. The exact details depend on the contract. For instance it may be for a limited duration or for life. Once the contract is signed, there's no backing out.
Because no one needs human workers, contract slaves are used almost exclusively for personal service. Some serve like old fashion handmaidens and man servants. Others are treated like pets or toys.
People agree to become contract slaves for a number of reasons. The pay is generally far more than they could earn any other way. Those who choose lifetime contracts may be securing a better life for their entire family. There are also perks to living in a mansion, even as a slave. Contract slaves generally get better food and various other creature comforts not available to common folks. As well as expensive medical treatments that can keep one physically young and healthy almost indefinitely.
There are those who don't choose it, but end up as contract slaves anyway. They may be coerced into signing, or even simply kidnapped and kept using forged papers. This is illegal of course, but law enforcement rarely goes after the hyper-wealthy unless they have an air tight case.