This Vuser already started a transaction with the same name issue in Performance Center

It's most likely because we started two transactions with the same name and didn't finish the first before starting the second. If an issue occurs when using the TruClient logic to start/end transactions, the open transactions will fail. Every object or transaction that is open must be closed.

How to Change TLS Version in Jmeter? TLS Version Jmeter settings

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