just want to ask if there's any API that I can use to send money from card to paypal account. It seems that funding_source of paypal payout API is only using paypal balance.
Also, another question, can we create invoice using personal account as the invoicer. I've been trying it and the response is always user_not_found.
Sending money from a card to a PayPal account is...making a PayPal payment? You can do that with a payment link, something like https://www.paypal.com/webscr?cmd=_xclick&item_name=sending_money_from_my_card&amount=100¤cy_code=USD&business=paypalaccountreceiver@emaildomain.com
As for invoicing with a personal account, has the personal account confirmed their email in PayPal? That is the most important thing. If it still doesn't work, simply upgrade it to a Business account. There is no reason not to do so unless it's from a country that doesn't support business accounts or doesn't support receiving PayPal payments (which there are a few)