Zohoapis.com Returns OpenSSL alert bad certificate

We are using PHP (Laravel) with Guzzle and calls to the API via Zohoapis.com are returning:

cURL error 56: OpenSSL SSL_read: error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate, errno 0 (see https://curl.haxx.se/libcurl/c/libcurl-errors.html

It seems the certs on that site are self-signed by Zoho. We note this error on both local environments and in Heroku.