Hey, catskittensjohnson (that's in the running for excellent username of the year!). It sounds like you're bumping into trouble trying to follow this process: Mobile Device Unlock: LG Stylo 2 PLUS. Have you tried pulling up the unlock app and walking through the process with a WiFi connection and/or your T-Mobile SIM, rather than a non T-Mobile SIM? If the phone's not successfully unlocked yet it may not have the data connection necessary to complete this process without an active TMO SIM or WiFi connection. I'm also a little concerned about the rooting that you mentioned -- have you already performed this? That might actually impact the unlock app's ability to work (not to mention voiding the warranty on your device), so if you haven't tried that yet, I'd definitely recommend holding off! Lastly, one thing I can also recommend is a cache wipe. Stale data from unsuccessful attempts can hang out and cause trouble.
If you could give this a shot again, I'd do the wipe first, and then insert an active TMO SIM and/or remove any SIM and connect to WiFi, and then follow the steps. Please let me know how that goes. Thanks!
Just wanted to check in on the advice Marissa provided above.