Issue 1: I can't open my certificate files
If you need to copy & paste the content of your certificate files into any type of user interface (e.g. the user interface of your hosting provider), you can open both the .crt and .key files with any text editor of your choice, e.g. "Notepad" on Windows or "TextEdit" on Mac OS.
Issue 2: The certificate has the wrong file format
For some servers, such as Microsoft IIS, it is required that certificate files carry the .pfx file format. To resolve this issue, please navigate to the following StackOverflow link and follow the instructions shown in the thread: StackOverflow Article
Please find below an excerpt of the resolution described on StackOverflow:
You will need to make sure you downloaded the correct certificate files and run the following OpenSSL command:
openssl pkcs12 -export -out crt_bundle.pfx -inkey private.key -in certificate.crt -in ca_bundle.crt