u/Equivalent_Twist_336

I have an iPhone 13 Pro Max I’ve had for a while now and I’m trying to be able to put in a SIM card from T-Mobile that I have but I always get this message [SIM Not Supported
The SIM that you currently have installed in this iPhone is from a carrier that is not supported under the activation policy that is currently assigned by the activation server Yada Yada Yada] but I know there is a way to unlock it for free (I hope) and be able to put in this T-Mobile SIM. I believe the information I gave with the iOS version and model should be a good help for this.