Following as I am also having that issue!

It should be the phone number of your home internet line. If that’s not working I would contact Tmobile customer support to sort this out.

Same issue. It asks for “mobile number” so it shouldn’t be the home internet number assigned. That being said, I tried that too, to no avail. Any resolution?

I’m having the same issue, same error message. Used both cell number and internet number both don’t work. 

I have same issues. And my lines are working. So now what???

It could be the browser you’re using.  I typically use mozilla but when I log into tmo with it, it tells me something’s gone wrong and to try later.  I logged in using chrome and I could enter data and it would accept them.  Try it.

Thank you for all the responses to my question. It appears the Internet has a different phone number. Attached to it versus the cell phone number It was asking for. I got my visa rebate, so thank you all :) 

I got the card information and activated it. But when I use it, I get told there are insufficient funds. I haven’t used any of it. What do I do?