US Payer Ecosystem: Medicare, Medicaid, Commercial (BCBS, Aetna, Cigna, UHC), HMO/PPO plans, copays, deductibles, COB. Credentialing: NPI, CAQH, payer contracts, EDI/ERA/EFT setup, re-credentialing. Front-End RCM: Patient registration, real-time eligibility (270/271), prior authorizations. Medical Coding: ICD-10-CM, CPT (E/M), HCPCS Level II, modifiers, LCD/NCD medical necessity. EHR & Clearinghouses: Navigation (Epic, Athenahealth, Kareo), 837P/837I claim scrubbing (Availity, Change Healthcare). Portals & Payment Posting: Payer DDE, ERA/EOB interpretation, manual/auto payment posting, write-offs. AR & Denial Management: 30–120+ day aging, CARC/RARC code analysis (CO-16, CO-45), appeal drafting. Compliance & Career Prep: HIPAA/FWA standards, resume building, mock interviews for AR & Billing roles.