Is a written contract necessary for freelancers working with online companies in Thailand?

I’ve been reading a lot of posts lately, and it seems like everyone’s talking about contracts.

As a freelancer working with an online company, I keep wondering—how does the idea of a contract apply to someone like me?

I do have proof of my work:

• My profile on the platform

• Screenshots of the website where I work

• Financial transfers and payment history

But there’s no official written contract between me and the company.

Is having a contract a must in freelancing?

Or are there other valid ways to prove work relationships and protect your rights?

Would love to hear thoughts from fellow freelancers or legal experts in the space.