Solution:
1. Verify that you have an activated Micro SIM from a valid GSM carrier. ZenFone 2 SIM type is a (Micro SIM).
2. Turn off the ZenFone 2 by holding down the power button for several seconds to get the power off menu. Tap (POWER OFF) and then (OK) to shut the device down.
3. Look for a groove/seam near the corner on the side of the device. Closer to the Micro-USB port.
4. Using fingernails, carefully pull back the groove and work around the edges and corners to pull out the back plate.
5. Take the Micro SIM card and carefully insert it into sim slot 1. Do the same for sim card slot 2 if using a secondary activated sim card. There will be a slight spring click once inserted all the way in. (Please note: Sim card slot 2 can only receive 2G voice and basic instant messages while sim card slot 1 can receive full 4G/LTE/3G/2G service).
6. Once the Micro SIM(s) are inserted along with a Micro-SD card (If applicable), then fold the back cover to align it with the front side. Volume keys and camera cut out aligned as well. Then carefully snap the back cover along the edges together with the chassis until all the edges and sides click into place.
7. Hold down the power button for several seconds to turn back on the phone. Then check for cellular service.
