Hi Sam,
Check Activity log to find which TPA got executed
By default Unknown/Unknown TPA will get executed for any inbound/outbound TN Transactions, if you want set a specific TPA. you need to create TPA and get it execueted in code based on agreementID and map the values.
Check TN Concepts guide for more reference
#webMethods#B2B-Integration#Integration-Server-and-ESB