Does a UMI in production mean the same as Working Interest?

I was sent a lease that I did not accept, and I returned it with my preferred changes. I never heard back.

Two years later I started getting royalties on the wells involved. The production company suddenly realized they didn’t have a signed lease, so they sent another lease to me, encouraging me to just sign it. I called a lawyer in TX to ask if this was legal and he said no. He encouraged me to just become a co-owner of the wells.

After some silence and delays, they finally sent me a division order for a UMI payout. Now it’s tax time, and my accountant surmised that, for tax purposes, I am a working interest owner, which means I am taxed 15% more for the income from that lease, as I am a business co-owner. I am not sure I am a working interest owner, since I didn’t put anything down on this lease.

I’m not sure what my position is. Do I need to get liability insurance? Form an LLC? What is this situation called?