I’ve seen the “The number parameter is required” error in the past when the Stripe keys are invalid, I’d suggest trying to generate new API keys in the Stripe portal to see if it helps.
Also, check the browser console for any JavaScript errors.
So I did check the browser console for Java Script errors and indeed this is what helped me to fix my issue.
I have both http and https enabled for my selfhosted invoiceninja.
Customers who came in on http are not allowed to enter in the credit card information which in turn gave the stripe error. I’m sure this was by design from the developers (and rightfully so).
So to fix my issue, I created a redirect on port 80 to 443 within our webserver.