1) what other sources of funding would the FBI use?
2) Why wouldn't they offer money to an informant? It's a common practice.
3) He was offered but wasn't paid. Meaning he was unable to corroborate or refute the claims he reported in the dossier.
4) he was not acting as an agent of another government, but as a citizen of another country. While you may think this is no big deal, it is significant.
This is nothing like Watergate.
Do you even know what happened at Watergate?