Heroku ssl certficate not switched with custom domain - ssl

Question

I have a heroku app (whatever-app-11123) and I want to use a custom domain through ssl (https://myapp.co).
I have bought the certificate and followed all the instructions provided by heroku.
Strange thing is that https://whatever-app-11123 is displaying the myapp.co certificate and https://myapp.co is displaying the *.herokuapp.com certificate.
I need this to be the other way around : myapp.co with the myapp.co certificat.
Any hints on how achieving this?
Results of different commands :
herok:certs
Endpoint Common Name(s) Expires Trusted
--------------------------------- ---------------------------------------- -------------------- -------
whatever-app-11123.herokuapp.com myapp.co, www.myapp.co 2017-02-12 23:59 UTC True
curl -kvI https://www.myapp.co
* Adding handle: conn: 0x7fbd03804000
* Adding handle: send: 0
* Adding handle: recv: 0
* Curl_addHandleToPipeline: length: 1
* - Conn 0 (0x7fbd03804000) send_pipe: 1, recv_pipe: 0
* About to connect() to www.myapp.co port 443 (#0)
* Trying 46.132.168.142...
* Connected to www.myapp.co (46.132.168.142) port 443 (#0)
* TLS 1.2 connection using TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
* Server certificate: *.herokuapp.com
* Server certificate: DigiCert SHA2 High Assurance Server CA
* Server certificate: DigiCert High Assurance EV Root CA
> HEAD / HTTP/1.1
> User-Agent: curl/7.30.0
> Host: www.myapp.co
> Accept: */*
>
< HTTP/1.1 302 Found
HTTP/1.1 302 Found
* Server Cowboy is not blacklisted
<
* Connection #0 to host www.myapp.co left intact

Answer 1

Here's the answer: check your DNS redirection. Make sure it is a CNAME type and MOST OF ALL (what I did wrong) the redirection should be :
www.myapp.co -> whatever-app-11123.herokuapp.com
myapp.co -> whatever-app-11123.herokuapp.com
and not
www.myapp.co -> myapp.co
myapp.co -> whatever-app-11123.herokuapp.com