Check if your device is registered with our certificates
Follow this Guide: Click Here to open https://udid.tech/ after that click "Get your UDID now, then click "Download" after that click Allow then Close. Open the Settings app on your iPhone scroll down to General then find VPN & Devicemanagement and go There. You will see a Downloaded Profile containing Udid.tech in the title, click on it then at the top right "Install" enter your Passcode if you have one then click Install again on the action sheet. Click on the UDID Field to copy your UDID, this is what an average UDID looks like:
UDID Format: 00008030-000A1234567890123456