Just add a new line in your config/reverb.php to specify the location of your intermediate certificate:
'options' => [ 'tls' => [ 'local_cert' => env('SSL_CERTIFICATE_CER'), 'local_pk' => env('SSL_CERTIFICATE_KEY'), 'local_ca' => env('SSL_CERTIFICATE_CA'), 'verify_peer' => false, ], ],
The key is the line ‘local_ca’ => env(‘SSL_CERTIFICATE_CA’)