Thank you for your post and welcome back to the Community Forum!
In general, if the payment has been completed, you would not be able to cancel it. However, if you paid for 'Goods and Services' as it seems, you would be covered in case you do not receive the item. IF this happens, you can file a dispute for an Item Not Received. If the seller does not collaborate, you can escalate the dispute to a PayPal claim within 20 days. Please note that you can only do so after 7 days from the date of the purchase.
For future reference, I would recommend always using the option 'Goods and Services' and the option 'Friends and Family' would not be covered in case you do not receive the item. More information here.
I hope this helps!
... View more