In no way proven, or even credibly accused
- Foreign actors gained influence to American policy for money
- Joe profited from from selling out the USA
"Credibly" just means "believably".
There are a couple of things - according to people with experience - that investigators looking at bribery/laundering recognize as red flags:
- Family members of a prominent politician receiving large amounts of money, without any apparent goods/services worth exchanging, might be bribery
- A network of companies in which money swishes around to no obvious purpose might be laundering
One specific accusation is that Joe Biden was paid to help Burisma, and that one of the things Biden did was pressure Ukraine to fire Shokin, in order to get Shokin out of Burisma's hair.
Enough of the pieces are in place - the money, the companies, the players, the downward slide of denials from "Joe doesn't talk with Hunter about business" to (briefly) "Joe is not in business with Hunter" to "Joe was on several calls with Hunter's business partners, but just to make small talk" - that many people do find the theory credible. Polls suggest half to two-thirds of Americans think something rotten involving Joe is at the heart of the matter.
I suppose most Americans fall into one of 3 categories:
a) believe Joe's presence on the phone was clarifying that Joe was part of the deal
b) believe Joe's presence on the phone was totally innocent
c) as (a) privately, but (b) publicly because of political exigencies
The incredible theory isn't the bribery theory; the incredible theory is that good old Joe was just on the calls for no particular reason. And for some reason, all of the pieces are just innocuous meaningless little things that don't merit investigation.