I think there are two somewhat separate issues here. Not completely separate but it is helpful to think of them as distinct. One is any financial relationship(s) that existed between Trump and the Russians prior to the campaign.
The second is the intricate dance that occurred over the course of the campaign that led the two parties to develop a symbiotic relationship. Russian help in various forms including leaking the hacked emails. The Trump campaign changing the GOP platform on Ukraine and holding out the prospect of an easing of sanctions. This intricate dance had many facets, one of which was the use of Papadopoulos as a point of contact.