Exam CIPP-US topic 1 question 19 discussion

SCENARIO -
Please use the following to answer the next question:
A US-based startup company is selling a new gaming application. One day, the CEO of the company receives an urgent letter from a prominent EU-based retail partner. Triggered by an unresolved complaint lodged by an EU resident, the letter describes an ongoing investigation by a supervisory authority into the retailer’s data handling practices.
The complainant accuses the retailer of improperly disclosing her personal data, without consent, to parties in the United States. Further, the complainant accuses the EU-based retailer of failing to respond to her withdrawal of consent and request for erasure of her personal data. Your organization, the US-based startup company, was never informed of this request for erasure by the EU-based retail partner. The supervisory authority investigating the complaint has threatened the suspension of data flows if the parties involved do not cooperate with the investigation. The letter closes with an urgent request: “Please act immediately by identifying all personal data received from our company.”
This is an important partnership. Company executives know that its biggest fans come from Western Europe; and this retailer is primarily responsible for the startup’s rapid market penetration.
As the Company’s data privacy leader, you are sensitive to the criticality of the relationship with the retailer.
At this stage of the investigation, what should the data privacy leader review first?