The image has to be focused, clear, and legible. There is no live-chat or phone support because it is cost prohibitive. You can contact support here.
If you want to have an item shipped with the peace of mind of the "Buyer Protection" plan in place (just in case), you will have to complete the TruYou process, unless you and the buyer come to some type of other agreement outside of OU. To clarify, I am not endoring this method, but you can use your own judgment
Offerup has decided to use Stripe as the payment processor, since it was most likely the cost efficient alternative to Paypal (until recently, was owned by eBay...a competitor to OU). IMO, Adyen is the most versatile. payment processcor.