Thanks for sharing your experience and solution, @jpringle!
To summarize, if you use Android devices with versions < 7.1.1 AND they connect to a server that uses a certificate issued by Let's Encrypt :
- If you can upgrade to Collect v1.29+ before June 2021 (tentative date from Let's Encrypt), do so, and no other changes are needed.
- If you can't upgrade to Collect v1.29+ before June 2021 but you will be able to before January 2024 or won't be using older Android devices by then, you can continue to cross-sign your certs until you can upgrade Collect. @jpringle's instructions may be helpful if you're on Digital Ocean. Otherwise refer to the Let's Encrypt post
- If you can't upgrade to Collect v1.29+ before January 2024, I believe you will need to switch to a certificate authority other than Let's Encrypt. That's far enough in the future that things may very well change a lot before then.