Thank you for helping me with this! (And on a Saturday ta-boot!). That helped narrow it down. It’s working now. HURRAY! (Deactivating Root Folder BulletProof Mode worked. So, out of curiosity, I deactivated, uninstalled, and reinstalled BP security. Then placed the custom code back in and clicked the activate button and what not.) Transaction went through on live paypal, with no 403 errors.
Thank you! Thank you!!!!!!!!!! 😀