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I am trying to add a subdomain for an api. The api is built using api-gateway/lambdas and therefore lives in aws. The url provided for the api is of the form: <random-hash>.execute-api.<region>.amazonaws.com. When forwarding the subdomain to the AWS url, I receive a forbidden, I believe because the AWS domain doesn't match the squarespace certificate. I then tried using Route53 to manage the dns of the subdomain. They provide nameservers I can use for the dns lookup, but there is not place to add nameservers for the specific subdomain in squarespace.

Additionally, I created a cert for the subdomain in AWS, and then tried to add the cname validation record to the dns settings in squarespace, but the put request fails saying, 

Quote

Custom record not saved

We were unable to save this record. Try again later. If this problem continues, contact Customer Support.

 I was hoping for some direction on how to get this setup correctly while keeping the domain hosting within squarespace. I basically need, api.<domain>.com to be a subdomain pointing to <random-hash>.execute-api.<region>.amazonaws.com, from squarespace dns. I can move all dns over to AWS, but I was hoping to avoid that.