When you create SFTP endpoint into VPC I believe you must provide EIP(s) for it. Details are shown in this blog post. https://aws.amazon.com/blogs/storage/use-ip-whitelisting-to-secure-your-aws-transfer-for-sftp-servers/
Can you use a VPC endpoint with internet-facing access?
According to the above blog, if you choose a VPC endpoint with internet-facing access you can attach Elastic IP addresses to the endpoint. These can be AWS-owned IP addresses or your own IP addresses (BYOIP). Elastic IP addresses attached to the endpoint don't change.
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