Every social media platforms has different limitations for image size, resolution, dimensions, and aspect ratio. Especially Instagram's limitations are quite limited. When you try to publish a content which has images, RADAAR tries to prepare your images according these limitations for each platform.
If you see a white frame around your image when your content is published, it is because the technical specifications of your image is not within the limitations of that platform. And RADAAR has optimized your image for that platform so that you don't get any errors. That's why you see a white frame around your image.
If you don't want to see a white frame around your image, before uploading your image to RADAAR, please try using an image editor (For example: Photoshop) to convert it to the limits of the platform you want to publish and upload it to RADAAR: https://www.radaar.io/121-resources/388-blog/1614-social-media-image-sizes-in-2021/