Good Evening @Seller_itDcIupzbDnhS,

I just wanted to stop by as I have seen other videos on the platform with the black bars the sides that were also horizontal on detail pages as well, so I believe this behavior is normal however, based on the help page below there might be something else going on.

-->HERE<-- is the help page that was mentioned to you in the rejection message. I wanted to highlight the latest guidelines as of October 2024:

3.14 Video and Video Posts Guidelines

General guidelines

Sponsored Brands Video and Video Posts allow you to engage your customers by including compelling videos. Video can be in vertical (9:16) or horizontal (16:9) format under Sponsored Brands video, and vertical (9:16) only under Video Posts.

The video in your ads must be relevant to the product or brand and lead to a contextually relevant landing page.

Video asset requirements

Please ensure that your video complies with the following guidelines:

• Letterbox or pillarbox formats: Videos must not have continuous bars on any side of the video content. If they only appear in a few frames or the end card, this can be approved.
• We do not permit blank or black frames at the start or end of videos.
• Video ads cannot end in ways that truncate a description (voice over, speech or written text) in the middle of a sentence.

For Posts caption policies, please see here.

Please let me know if you have any questions regarding the content I have shared above or you can reach out to Advertising Support at any time. I hope you have a lovely rest of the week and take care. 😊

Sincerely, Cooper_Amazon