Is it POSSIBLE that the brand has sent Amazon a “whitelist” of approved sellers and did not have you on it?
More and more brands are providing such a “whitelist” of their approved sellers and if YOU are NOT on the list you will be stopped in your tracks and probably hit with an IP violation.
I had one of my brands stop me because they CHANGED the company they hired to screen sellers. The NEW screener did not recognize my Amazon store name because I do all my purchases under a different LLC. It took a couple weeks to get straightened out and no problems since then.