This is an advanced configuration option. Did you follow all the steps in the docs? https://docs.getodk.org/central-install-digital-ocean/#using-a-custom-ssl-certificate
I would also read through this thread and the threads it links:
This is an advanced configuration option. Did you follow all the steps in the docs? https://docs.getodk.org/central-install-digital-ocean/#using-a-custom-ssl-certificate
I would also read through this thread and the threads it links: