PayPal has recently updated its privacy policies. Now, not all donors will have the option to pay via PayPal guest checkout, which means that those donors were to create a PayPal account to donate, in case they don't have one already.
We have checked with the PayPal team, and they have updated this. " The Guest Checkout process has a number of factors that go into it, including customer location, region of origin, transaction risk, funding source, etc. These factors are considered to determine whether a customer is eligible to use the feature for a specific transaction. The availability of the feature is no longer made universally available and is subject to a case-by-case basis."