I am subscribed to a matched betting service (I would link to it but its in Italian, I'm sure you can find plenty googling), I pay a monthly fee and they provide guides (on a daily base) and tools to take advantage of bookmakers bonuses. After you get the hang of it, it gets quite easy.

A few quirks: - Depending on gambling laws of your country, it might or might not be possible to do matched betting - It's not a constant source of income, it decreases over time as you can only exploit welcome bonuses once and bookmakers stop offering promotions to you after they realize you're not a fish. The year I started doing it I was over 4k euros yearly income, now I'm happy if I can get 2k. Still, I'm happy with the amount I get, its a good chunk of my income but for someone with a high salary might not be worth it. - The coronavirus pandemic slowed things down quite a bit, since currently there are few sport events. So it might be not the best time to start doing it.