Do you need to buy an expensive camera for fashion photography?

I’ll lay it plain and simple in the beginning, no you don’t. It's not about the camera. Purchasing a professional camera won’t instantly make you a better photographer. In fact, it won’t have any impact at all, to begin with.
Most cameras, DSLR and mirrorless alike, have incredibly good specs. Of course, a professional will have a higher quality than an entry-level one, but with the correct settings and light, you’ll barely see the difference.

It’s your knowledge and understanding of photography that will help you capture better images and that’s not something you can learn overnight. It takes time and dedication to master these skills.

The images on the right are from my Canon 1200D with an 18-55mm kit lens.

People don’t put enough emphasis on the fact that you can get better with older gear and learn so much better by using that first camera. If you’re not creating with the camera you already have, you won’t create anything with a more expensive one.

The only four main advantages of an expensive professional camera over an entry-level photography camera are:

1, Better Dynamic Range performance, so more detail in the photos
2. Better ISO performance, so less noise when shooting in a dark environment

3. More focus points, so better for a fast-paced environment like sports photography, wildlife photography etc.

4. Larger sensor size and higher resolution, so no surprises when getting very large prints of your photography, like on a billboard.

I am glad that cameras aren't "Pay To Win". It's so much more than the camera you own, it's about the creativity, the eye, the aesthetics, the edits, etc. All cameras are capable of great images.

As one of the famous photographers says: "The best camera is the one that you have now.", and that's true.