Do you have a function to check AWS account with vpc NAT gateway authorized IP?

I am inquiring about something special while uploading the file to the s3 web console.

Environment: aws(B), aws(A) other accounts.

Test 1 A. Test User (B) -> EC2 vpn(A) Connection -> B Web Console Connection -> s3(B) Web Console file upload is failing due to permission issues.

Test 2

B. Test User (B) -> B Web Console Access -> s3(B) Web Console File Upload Successful.

Note:

1. The Test user has S3 full permission on account B.
2. S3(B) No policies have been added to the bucket.

I was wondering if it's right to check the authorized IP used by AWS and give them a proper account!