Streamtip is not a payment processor, so we do not have the ability to accept any payment method. If we did, we would need to be responsible for tax accounting for all users, which isn't feasible for a free service. Therefore, we integrate third party processors like PayPal and Coinbase for people to tip through, and we simply track the payments being sent.
TwitchAlerts, as far as I've been made aware, only supports the same payment method we do, PayPal. GamingForGood piggy backs on G2A Pay, which is not a payment provider we are looking to integrate with, sorry.