1)Firstly,you should look at the top left corner to see if the signal bar or 4G appears.
If it doesn't appear then it's not recognizing the card, and at this point you need to check if you're inserting the card in the right direction.
video tutorial: https://carlinkitcarplay.com/blogs/t-box-multi-language-tutorials-for-factory-wired-carplay/what-i-can-do-if-the-sim-card-cant-work-after-inserting-it-into-the-t-box
2).Secondly,If insert the SIM card and recognize successfully, but fail to access the Internet.Please check the APN information of the SIM and fill in the information inside the box.
How to do:
Open Setting-Access Point Names-Click on the plus sign in the upper right-Modify name and APN-Save
Video tutorial: https://www.youtube.com/watch?v=b44jy5xnXIQ
