If you haven't altered the default settings, JMeter should be using the TLS protocol in general, and TLSv1.2 specifically. If this doesn't match your payment gateway pr your application settings, change https.socket.protocols to match what your application requires.
You can add the following lines to the log4j2.xml file to get debugging output for SSL and network things.
<Logger name="org.apache.jmeter.util.HttpSSLProtocolSocketFactory" level="debug" />
<Logger name="org.apache.jmeter.util.JsseSSLManager" level="debug" />
<Logger name="org.apache.http" level="debug" />
<Logger name="org.apache.http.wire" level="debug" />
and change the below line in system.properties file:
javax.net.debug=all
Note: Must and should restart your Jmeter to update the above changes