PayPal adaptive guest payment requirements

We are using the adaptive payment API to setup a payment between 2 of our users. The receiver user has a paypal account, the source (the one who pays) doesn't. We don't use any chained or parallel payments just simple tranffer from A to B. We'd like to allow the source to pay with credit/debit card. The problem is that in some cases its allowed, and in some it isn't.

We found this document about the subject but it looks outdated, since in the limitations section it says:

Cannot be made to a personal or un-registered PayPal account

I have a personal account and it works with that but with my colleague's personal account (different country) it doesn't.

Not available if the API caller passes an email address in the request envelope.

This is very vague. Pass where? We use the email address in the pay request but it works in some cases.

Could anyone give some up-to-date info about this subject?

Here are my findings together with PP_MSI_Colin's answer:

Documentations

Guest payment - integration guide (UI is different now)

Guest payment - adaptive payment

Account optional settings

Requirements

• Upgrade to business or premium account.
• Make sure the email address is verified.
• Make sure that on this settings page the Paypal account optional setting is ON.

Limitations, exceptions

• In EU, this option is limited to 10 payments/card
• In some countries (tested in Hungary) a personal account can also receive guest payments.
• In some countries it is always disabled. No official list found.

Logic

Even if it is enabled for a user, it is up to Paypal if they show it or not. Where its enabled it also depends on the paying user. If Paypal finds (from cookies, etc) that the user has a paypal account they don't show credit card option. To test it try to pay in an incognito window. PayPal’s fraud prevention measures can also cause the guest checkout to not be displayed in certain scenarios