Make sure that you have configured cafile inside php.ini

[openssl]
; The location of a Certificate Authority (CA) file on the local filesystem
; to use when verifying the identity of SSL/TLS peers. Most users should
; not specify a value for this directive as PHP will attempt to use the
; OS-managed cert stores in its absence. If specified, this value may still
; be overridden on a per-stream basis via the "cafile" SSL stream context
; option.
openssl.cafile=/etc/apache2/cacert.pem

Download cacert.pem from https://curl.haxx.se/ca/cacert-2020-01-01.pem
More certs: https://curl.haxx.se/docs/caextract.html