@onlymega i believe Braintree will not accept the purchase without payment details, what you can do
1- create a trial on your website by using
Spark::useBraintree()->noCardUpFront()->trialDays(30); in SparkServiceProvider
2- remove/comment
Spark::plan('Starter', 'starter') ...
which will allow users to register without providing a credit card and having a trial of 30 days.
@onlymega can you please share with me how you set up Braintree on Spark? I'm having a trouble when using Braintree instead of Stripe.