Actually, what your article stated was...
The FEC fined both organizations after a pair of now years-old complaints — one from the Campaign Legal Center and another from the conservative Coolidge Reagan Foundation — alleged that the party and campaign reported payments to the powerhouse Democratic law firm Perkins Coie as legal expenses, when in actuality some of the money was earmarked for “paying Fusion GPS through Perkins Coie to conduct opposition research on Donald Trump”
Lemme explain that to ya since you're too stupid to understand that without my help. The fine was for not reporting money paid to Fusion GPS. Which was a violation of the statutes specified in the letter, linked in your article.
52 U.S.C. § 30104(b)(5)(A)
C.F.R. § 104.3(b)(4)(i)
^^^ Which have absolutely nothing to do with foreign agents.