Thank you for reaching out to AWS re:Post, I understand that you are having trouble with your customer accessing your hosted site.
From my investigation there could be a problem with you IP addresses allowed to access your site through your Network Access Control List.
To add or delete rules, Choose Network ACLs under VPC -> In details choose inbound rules and Edit -> Under rules choose HTTP -> In Source or Destination choose CIDR range of IP addresses or just the customer’s specific IP if you want -> Select ALLOW to allow specified traffic -> choose Save to finish adding your rule
Please take a look into this document for a deeper dive into your query. 
Please contact if you have any further questions, or reach out to us via a support case to facilitate a discussion on the specifics of your resources.
Hope you have a wonderful day.
Control traffic to subnets using Network ACLs - https://docs.aws.amazon.com/vpc/latest/userguide/vpc-network-acls.html#nacl-tasks
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