Braintree and Bubble API

I am building a combined Bubble and Windows application. The Bubble app allows users to sign up for a service that allows them to download a Windows app and perform admin tasks on their machine. I have added Braintree and I can charge the user in the Bubble app or add them to a subscription. My issue is that i would like to charge per admin task performed. For instance I would like to perform a set of tasks on the Windows client machine and if successful the Windows app will call the Braintree plugin on Bubble and charge the user $x.

I can make subscriptions work on a monthly basis and I can charge the user a fixed amount through the Bubble app but I am struggling to charge the user from the Windows app. this is because they have to enter their card details as part of the Bubble workflow. Is there anyway I can pass the card details to the workflow from my Windows app? I will be using HTTPS so security should not be an issue.

Alternatively, can I store the users card details in Bubble in a secure manner so that I can issue an instruction to charge the user directly from the Windows app?

Not really, as the card details are stored in Stripe/Braintree, not Bubble.