Make sure SIM cards have been activated by checking their status on Twilio while attached to a board and modem known to be working.

Here's a link to where you can check a SIM cards connectivity in Twilio: https://www.twilio.com/console/wireless/... The page should look like the first photo

Type in the first two rows of numbers on the SIM card in the search bar to find it

Once at the page for your specific SIM card click on connectivity and check to see if any red shows up on the timeline. An example of this can be seen in the second photo.

It takes a while for the connection to register on Twilio so wait a while and keep refreshing before determining the SIM card is not active.

Make sure the modem has been tested

Make sure the little board has been tested

Make sure the big board has been programmed