Unlocked, but simlock or "international" issues? (opens in new tab)

I bought an iPad mini \(A17 Pro\) wifi\+cellular secondhand off of Facebook marketplace\. The seller disclosed that it had some sort of simlock with t-mobile and that's why he was selling and had purchased another\. I don't really care because I can do most of what I want with it using wifi anyway, but cellular would be a nice-to-have on a cheap plan like Mint mobile\. I tried to get it to activate on Mint but had numerous problems and a promise of a callback after escalation that never\.\.\....