Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. crt.sh | example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
Well, you haven't given us much (anything, really) to work with, so the best I can say is, "whatever you did to get the cert in the first place, do it again." But it's been expired for over a month--why is it just now a problem?
I agree with danb35 and also why can't you use the Sectigo or Google cert which are both still valid? That at least would give you some time to get your Let's Encrypt requests working again
It looks like you are using Wordpress as your website content management/publishing system and your web server software is nginx. You should investigate whether you used a Wordpress plugin to get your last certificate and if so look at the options/logs etc for that. If you use a command line tool such as certbot or acme.sh you will need to repeat what you previously did to refresh you certificate. For instance Certbot has a "renew" option but you may also have to restart your web server for the certificate change to take effect.
Best to get a local web consultant to help if you don't know how to do this.
The domain uses Cloudflare and while the domain is not currently proxied, those may be employed as Cloudflare edge certificates which would make their keys inaccessible.
Sure, I guess they could have been proxied at Cloudflare on those dates. But, I thought when Cloudflare uses Sectigo certs they are 90 day certs. The one here is 1 year.
