We would need more info to go on, such as :
Have you bought a plan and activated your SIM card ? Check your Smarty account dashboard to check that you have an activated SIM card and active plan.
Are you trying to use your SIM in a phone or mobile router ?
Are you trying to use the SIM in the UK or overseas ? (If overseas, the APN in your device needs to be changed to ‘mob.asm.net’)
