Am I to guess it is an Android phone. Visible has a list that consists of IMEI numbers of phones, it is mostly made up of phones that have been sold through Visible in the last year. I bought a phone here when I joined in 2021, and it works fine on the old plan that I am still on but if I were to change to one of the new plans my IMEI number comes up as not compatible. It is easier and more profitable for Visible to sell you a phone when you port in than it is to take the time and add more IMEI numbers to the approved list. There has been at least one that has activated a card in a compatible phone and moved it to a noncompatible phone and it worked. I have not saw where anyone has actually activated a SIM in a noncompatible phone. There is a way to get around the not compatible issue to get a SIM card by Googling IMEI number generator and selecting a Pixel or Samsung phone from the list and generate some numbers and find one that will allow you to order a SIM. It is unknown if you could actually activate it.
Another way would be is buy the cheapest phone Visible sells and activate the card and then move it to the phone you have now.
