Please check if the service start date has arrived.
For example, if the your selected service start date is August 1st, even if you try to use it on July 31st, you will not be able to access the service. (Based on EST)
Please check the coverage map using the zip code to confirm if the area where you are located is within the service coverage area.
Coverage Map
Please check your device model and its purchase source.
For instance, if you have an iPhone 14 Pro Max, it is compatible with both regular SIM or eSIM. But if you did not purchase it directly from Apple store and bought it from a retail store, there is a possibility that the device may be locked.
Please try restarting your device. Then removing the SIM card and inserting it again.
Please check the APN setting. APN setting