If you have cPanel hosting, please consider ask the host to use AutoSSL to obtain FREE certificates instead of manually obtaining it.
Because in this setup, You'll need to repeat the process every 2 months (minimum).
I don't think the company will actually use your chain file, because cPanel does have a feature to auto load your certificate chain. Also, if you obtained the certificate using ACME client, those clients will typically provide a chained certificate for you.
Just in case there aren't anything, you can use this website to generate a complete chain: Warning: Third-party Internet resourceshttps://whatsmychaincert.com/