What is wrong with this sequence of TCP 3 way handshake?

edit

I have a client (192.168.1.129) sending data to my server.

"26","10.671930","192.168.1.129","52.54.68.0","TCP","66","57835 → 443 [SYN] Seq=0 Win=8192 Len=0 MSS=1460 WS=4 SACK_PERM=1"
"27","10.688948","52.54.68.0","192.168.1.129","TCP","66","443 → 57835 [SYN, ACK] Seq=0 Ack=1 Win=26883 Len=0 MSS=1460 SACK_PERM=1 WS=64"
"28","10.689007","192.168.1.129","52.54.68.0","TCP","54","57835 → 443 [ACK] Seq=1 Ack=1 Win=65700 Len=0"

This is all fine. The next packet (Client Hello) is where the server goes into a server 500 error:

POST /sub_crud/Subit_backend/register HTTP/1.1
Host: www.substantiat.com
Connection: keep-alive
Content-Length: 79
Access-Control-Allow-Origin: *
Origin: chrome-extension://bdjgnodlhfmhghjhbkkkaaammfocdpib
X-Requested-With: xmlhttprequest
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36
Content-type: application/json
Accept: */*
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Cookie: XDEBUG_SESSION=XDEBUG_ECLIPSE; cisession=4ovqdcvlpmc21o90efdjd34hrm5b2qpp

{"lat":"41.0522371","long":"-74.0711244","email":"[email protected]"}HTTP/1.1 500 Internal Server Error
Date: Mon, 01 Oct 2018 22:55:13 GMT
Server: Apache
X-Powered-By: PHP/5.6.36
X-Frame-Options: SAMEORIGIN
Content-Length: 0
Connection: close
Content-Type: text/html; charset=UTF-8

I rebooted the server before running this. Is this a problem with the client's request or the server's response (Linux)?