Mattermost integration: certificate verify failed with internal CA signed cert (although curl from OS works)

Trying to add our mattermost server in the gitlab mattermost integration but I get:

Connection failed. Please check your settings. SSL_connect returned=1 errno=0 state=error: certificate verify failed (unable to get local issuer certificate)

Running on RHEL and we have added our corporate issuing CA certs to /etc/pki/ca-trust/source/anchors/ and done a update-ca-trust, if I test a curl it works fine …

Doesnt gitlab use the OS certificate trust store?