A customer done a purchase transaction on my CF 2-step order form via PayPal and it went through smoothly and was redirected back to my OTO1 page.
When the customer clicked on the OTO1 page buy button, the order was not being processed and according to the sales tab on my funnel, the OTO1 order has failed.
Please help as I am really lost and confused and do not know what to do next.
Also, is it necessary to setup the Paypal App V2 in order to have a seamless OTOs/Upsells transactions via Paypal?
No not necessarily, PayPal v2 does not need doing the 1-Click upsell hack you already did, and there isn’t any big difference when it comes to upsells other than that which you already did.
For the fact that PayPal doesn’t work on your OTO page, you need to share or private message me your Order form and OTO Urls to give them a try and see what could be wrong, the common issues we find most do are: