As a Namecheap user, you would be able to more easily use one of the ACME clients which supports issuing wildcard certificates automatically via the Namecheap API.
One option: dnsapi · acmesh-official/acme.sh Wiki · GitHub
However, there is one particular pain with the Namecheap API, and that's actually getting access to it. Here are the qualifications:
To qualify, you must have: Account balance of $50+, 20+ domains in your account, or purchases totaling $50+ within the last 2 years.
I have to come clean, I wrote that blog post at a time when I had a less than stellar understanding of all things Certbot. It could still work in theory but I have to discourage its use, just because over the long term, hacks like this tend to crop up with problems. I thought I had since delisted the page, but apparently people can still find it.
If you have access to the Namecheap API. try use a supported client like acme.sh as I linked above, or others who also have support, like lego, Posh-ACME etc.
If you don't have access to the Namecheap API, you can try something like acme-dns or try choose another DNS host like Cloudflare or others that can easily work with ACME clients.