Since I can no longer use Paypal; I moved all my commissions of any kind to Artconomy
https://artconomy.com/profile/Osito/about/
Artconomy is a commission platform made by furries, and it works with an escrow system in which the artist doesn't get to start the work until payment was made but artist doesn't get the payment from the platform until the final artwork was delivered; this is called Artconomy shield and it costs a fee, but is not abusive compared with other commissions platforms such as Fiverr and Skeb.
For now they just take debit/credit card payments, so keep that in mind.
They also provide with invoicing, I think (I just did one test commission there).
Here's a link to their FAQ if you want to know more:
https://artconomy.com/faq/buying-an.....ng/how-to-buy/