awsEndpointRequestId not being consumed by headers for HTTP APIGateway

Question

According the Customize HTTP API access logs, the logging variable $context.awsEndpointRequestId is populated from x-amz-request-id or x-amzn-requestId header.

I am directly hitting the my HTTP APIGateway endpoint by setting these headers, but the value is not being logged in the access logs. I am logging it as traceId.

The access log format is,

{
 "requestId": "$context.requestId",
 "traceId": "$context.awsEndpointRequestId",
 "ip": "$context.identity.sourceIp",
 "caller": "$context.identity.caller",
 "user": "$context.identity.user",
 "requestTime": "$context.requestTime",
 "httpMethod": "$context.httpMethod",
 "path": "$context.path",
 "status": "$context.status",
 "protocol": "$context.protocol",
 "responseLength": "$context.responseLength",
 "responseLatency": "$context.responseLatency"
}

This is the value being logged,

{
 "requestId": "Slmybhv2BcwEMDw=",
 "traceId": "-",
 "ip": "<source_ip>",
 "caller": "-",
 "user": "-",
 "requestTime": "17/Oct/2025:10:46:13 +0000",
 "httpMethod": "GET",
 "path": "/foo/bar",
 "status": "200",
 "protocol": "HTTP/1.1",
 "responseLength": "17",
 "responseLatency": "10"
}

I want to set a custom UUID4 as the endpoint request id which will be used to trace requests between services. What am I doing wrong?