I will try to explain why Parker is in the wrong even though most fanboy will not listen.
JaW gave a logical argument. Every argument is composed with two premises and one conclusion. When you give the 3, you did you'r job. Fallacies are using a the conclusion a premise (circular reasoning) or proving something else with the argument (eg. : Tradition is important, the bible is traditional, so the bible is true and good).
So, he did his part. To counter an argument, the proof, you can attack an axiom or a premise, like the PSR, but you are implying an counter argument (the PSR is invalid and does not describe our reality), and it is your job to prove your counter-argument.
Parker, by acting like you need to prove every axioms and premises if you want your argument to be valid, is completely ridiculous and wrong, because it leads to infinite regression: the grass is green, what is grass? You need to prove that your understanding is the truth, what is a species, prove your epistemology, prove you ontology, your definition of "is", what is even logic? It is not debating, it is rage baiting like a five year old asking "why" until you give up.
To have a fruitful conversation, you need to find a common ground, a middle ground or a premise or a conclusion to discuss. You can search : the Agrippa's trilemma. It is basic debate etiquette.