TL;DR: In case of doubt, install the certificate chain.crt

The following files are inside the zip file:
- certificate.crt: contains only the certificate with no intermediates or ca.
- intermediate.crt: contains only the intermediates and ca.
- chain.crt: contains the full chain certificate. This is certificate, intermediates and ca.

If Bighaiku stores the information about the private key, the following files are accessible:
- certificate.key: contains the encrypted private key. Use the passphrase on Bighaiku to decrypt it.
- certificate.pfx: contains the private key and chain in PKCS#12 format. Use the passphrase on Bighaiku to open it.