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Thanks for your response. My website is hosted on Google Cloud, and based on WordPress. All I am aware of is whenever anyone tries to access my website, the message says it is insecure and the https heading crossed out.
Is that shared hosting or do you have a VPS? I.e.: do you have administrator (root) access on the device? Or just a control panel? (2 more questions from the questionnaire...)
How did you get the first certificate in the first place?
Also, looking at your certificate history at crt.sh | dhchewins.com it looks like it always renewed every 2 months as planned.. What changed?
Then the first step is to determine which ACME client was used to get the certificate(s). You might want to start looking for a speciflc "SSL" plugin in WordPress. If that doesn't show anything, you might want to check your webserver configuration (which seems to be Apache, another question of the questionnaire...) for the SSLCertificateFile directive. Often the location of that certificate will point to a certain ACME client.
Then the easiest answer to your question might be to get that same web designer to help renew the cert.
OR for them to, at least, explain some of the unknowns to you [and in turn to us (if you still can't resolve the lack of automated renewing)].
Those seem contradictory.
It is difficult (from here) to know why it can't use what it claims to have just been made readied for its' use.
SSH?
If any case, can you show the directories created (and their permissions)?
And, can you also create a test text file in the expected challenge location?
Sorry. I don't know how.
Maybe it's all too technical for me.
Any idea what hosting provider Google Cloud is known for? None of the names presented as options ring a bell?
The first 2 bullets are about the local file system. The 3rd bullet seems to be an actual HTTP request testing the webserver, leading to a HTTP 404 file not found error.
Perhaps the Apache configuration is currently in a state not compatible with the Really Simple SSL plugin. However, I have no clue about that plugin and I'm not sure if @dinzc is able and/or comfortable digging into the Apache configuration using SSH.