@luuvuong to make things a little easier for you I am attaching 10kb and 50kb payloads that you can use with curl to manifest the issue.
10k.txt (10.0 KB)
50k.txt (48.8 KB)
It would be nice if you could run three commands to fulfill this request for info (using those files, without /etc/hosts):
Small POST
curl -v --data '{"dummy":"x"}' -H 'Expect:' https://acme-v01.api.letsencrypt.org/acme/new-cert -H "Pragma: akamai-x-cache-on, akamai-x-get-cache-key, akamai-x-get-true-cache-key, akamai-x-get-request-id"
10k POST
curl -v --data @10k.txt -H 'Expect:' https://acme-v01.api.letsencrypt.org/acme/new-cert -H "Pragma: akamai-x-cache-on, akamai-x-get-cache-key, akamai-x-get-true-cache-key, akamai-x-get-request-id"
50k POST
curl -v --data @50k.txt -H 'Expect:' https://acme-v01.api.letsencrypt.org/acme/new-cert -H "Pragma: akamai-x-cache-on, akamai-x-get-cache-key, akamai-x-get-true-cache-key, akamai-x-get-request-id"
(Expect included to disable curl’s Expect: 100-Continue behavior).