MURPHY, Circuit Judge. The plaintiff in this case—which we will call “United Allergy”—provides personnel and supplies to primary-care physicians so that the physicians may offer allergy testing and immunotherapy to patients. United Allergy charges the physicians a set fee for its goods and services, and the physicians, in turn, charge medical insurers for their own allergy care. According to United Allergy, though, several insurers conspired with each other and with the predominant allergy-care medical group to drive United Allergy and its contracting physicians from the market. United Allergy brought two antitrust claims against the insurers and medical group. Yet the antitrust laws permit plaintiffs to sue only if they have suffered injuries “by reason of” an antitrust violation. 15 U.S.C. § 15(a). And the district court dismissed United Allergy’s antitrust claims on the pleadings because it lacked “standing” to invoke this provision. The court then rejected United Allergy’s state-law claims at the summary- judgment stage. We agree with the district court’s results. In the process, though, we must clarify the nature of the antitrust inquiry. To sue under the antitrust laws, a plaintiff must show both that it suffered an antitrust injury and that the defendant proximately caused the injury. United Allergy’s suit flunks the latter element. Relying on proximate-causation principles, the Supreme Court has held “that indirect purchasers who are two or more steps removed from [an antitrust] violator in a distribution chain may not sue.” Apple Inc. v. Pepper, 587 U.S. 273, 279 (2019). And the same rule should apply in reverse to indirect sellers for antitrust violations that a group of buyers (like the insurers here) commit. United Allergy is also an indirect seller because it is “two” “steps removed from” the insurers in the distribution chain. Id. The insurers directly bought from (and harmed) the primary-care physicians by allegedly conspiring to fix their reimbursement rates and deny their claims. And that conduct harmed United Allergy only indirectly because it led the physicians not to pay United Allergy’s fees and to end their relationship. We thus affirm.