Error with Authorize.net

Got this error when trying to checkout with authorize.net. I am in "sandbox mode" with authorize.net

There was an error while processing your transaction: 103 (TESTMODE) This transaction cannot be accepted.

How can i test authorize.net in sandbox? Not sure what I'm doing wrong.

It's because your transaction key was regenerated so you need to update the configuration of the plugin with the new transaction key:
community.developer.authorize.net/t5/Int...-accepted/td-p/12890

I knew it had to be something simple! I had an extra character in the transaction key!