INVERTO cases are niche so dedicated material is limited.
Where to look. PrepLounge has procurement and supply chain cases, search by tag. Read INVERTO's public case studies and white papers directly on their website, the language they use is what they want to hear back. European MBA casebooks (LBS, INSEAD, HEC) often have stronger operations cases than US ones.
What to prep. Cost reduction in direct or indirect procurement, sourcing strategy, supply chain optimisation, procurement transformation, and negotiation cases.
Learn the vocabulary. Direct vs indirect spend, TCO, supplier consolidation, BATNA, category management, working capital.
Math is operational, cost per unit, total landed cost, payback period.
Show genuine interest in procurement.
Good luck.