OK, I finally found the problem, damn its stupid but it gives all kinds of errors on the screen.
I kinda went back to basics and checked the SSL certifcate for compliance. I have noticed that the certificate was for http://billing.x.com. Then I checked the .env file app path and found that the path there was http://www.billing.x.com
Eventhough I had included the www version of the sub-domain in my CSR , the issuer (Sectigo) did not issue the www for the sub-domain.
I have modified the path and removed the www, close all app and tried again and voila! Message gone.
So the lesson is when you install a purchased SSL certificate, ensure that both version are covered in your CSR request, otherwise you’ll get errors. I had included both but somehow they do not allow both.
Thanks to hillel for helping me and direct me!
Regards