Consider the common use-case of an account that is funded by a third-party - not the account owner (for example, workplaces, universities or donors). Currently this is very hard to do, since the payer must log into the account and enter credit-card or paypal details.
Here is an idea how to make it simpler. Create a form where the account owner can enter an amount to pay and then click a button that says "create payment link". Clicking this link will create a specialized hyperlink that encodes the accocunt id and the payment amount. The account owner will then email this hyperlink to the payer. Clicking the link will open a page displaying the account owner and the amount to pay. The payer will pay and the system will automatically send the money to the relevant account.