Clients are not required to accept proposals, sign contracts, or pay invoices via Stripe (credit/debit card), Paypal, or outside Bonsai.
The only case where a client needs to create a free Bonsai account is if they pay via ACH. In order to pay via ACH, they need to connect and authorize their bank account.
As a result, Bonsai needs to securely authenticate the client. It only takes 1 minute for them to create a free Bonsai account, and we do not send them any other emails or aside from the ones associated with your payment.