What firearms parts are prohibited?

[Rockscout]

I have been selling gun parts using paypal for 15 years. Today my account was limited for violation of the user agreement.

I am now barred from paypal for life, and my funds are being held for 180 days. There is no recourse for me. 

I have always been careful to not use paypal for the purchase or sale of firearms and ammunition.

The open-ended policy against "certain firearm parts and accessories", must be my violation.

What exactly are these "certain parts and accessories", if it were made clear I could have avoided this mess.

For those of you who are curious, I do trigger jobs, and sell picatinny rails.

[2AGuy]

PayPal is run by leftists and they signal their "I'm better than you" virtue by not allowing any transaction that has anything to do with God given Second Amendment rights.  This accomplishes absolutely nothing other than to proudly display their ignorance and bias, and irritate freedom loving Americans.  How many violent felons in prison do you suppose used their PayPal account to buy a weapon?  The folks in charge here are hopeless and pathetic.