Curl and SSL certificate expired

I have been using curl to upload data for years. Suddenly, some months ago, curl started to complain about the SSL certificate:

pi@raspberrypi:~/energy-meter/script $ curl -X POST ...
curl: (60) SSL certificate problem: certificate has expired
More details here: https://curl.haxx.se/docs/sslcerts.html

curl performs SSL certificate verification by default, using a "bundle"
of Certificate Authority (CA) public keys (CA certs). If the default
bundle file isn't adequate, you can specify an alternate file
using the --cacert option.
If this HTTPS server uses a certificate signed by a CA represented in
the bundle, the certificate verification probably failed due to a
problem with the certificate (it might be expired, or the name might
not match the domain name in the URL).
If you'd like to turn off curl's verification of the certificate, use
the -k (or --insecure) option.

To workaround temporarily this issue, I used the -k option. How to fix this problem in a safer way?

Thanks in advance.

Good day @LLandre

Thank you for sharing your question with the community,

We recommend you to search this message and its meaning directly in cURL, nonetheless we find that could be related with the RaspberryPi date, so please be sure the system time is correct.

All the best,
–Isabel