The SSL certificate verification error reported by cURL library indicates that the cURL client does not have the correct trusted certificates configured:
Uncaught exception 'Exception' with message 'cURL error while making API call to WePay: SSL certificate problem, verify that the CA cert is OK. Details: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed'
Typically, this means that you have a very old (pre 7.18.0) version of cURL (see explanations in cURL documentation). You should update your cURL package and check if it solves the problem by running the following command:
curl -G -v https://wepayapi.com/v2/account
If it works, then running a webserver or php-fpm restart will get everything sorted.
Otherwise,you can configure the trusted certificates manually as it is explained in this article.