What crypto are you trying to pay in? If BTC, probably cashapp or strike (if available in your country) is probably the most straightforward. Be forewarned: both of these are KYC (know your customer) apps, so if you are purchasing anything that could be nefarious or illegal, you WILL get caught. BTC is very traceable unless you go through WAY more hoops and steps.
If you are looking for anonymous transactions and trust the seller, sending cash is probably the most anonymous without a ton of steps.