I've got an offer in a field I was interested in (machine learning "researcher" for a computer vision application), but it was paying roughly half what I was ma

I've got an offer in a field I was interested in (machine learning "researcher" for a computer vision application), but it was paying roughly half what I was making previously as a backend dev, so I declined it. How I got the offer? Self-study, doing simple projects, working on my maths and stats fundamentals.