Large purchase: can you supplement PayPal credit with a debit payment?

Description

I am considering a large purchase and have a PayPal credit limit £100 short.
I have the entire balance of the purchase in high-interest savings – so I am not worried about making payments.
I am trying to build my credit utilisation history – as although my financial situation is good, I have rarely used a loan.
The purchase is not an official registered trader (it is something over Facebook Marketplace). I will not use Friends & Family.
As such I have a few questions:
Is it possible to purchase an item using (for example) a £100 debit payment and my full credit balance?
Is it possible to use credit when paying another user rather than a registered store/merchant?