Hi,
You can check my blog article referenced below.
When you get HTTP 500 with a TransactionID, the first thing is to lookup the TransactionID in the FWSTrace.log and understand what the problem is.
If the error is coming from IDP side URL, then the IDP side FWSTrace.log should be checked.
Federation Starters
If the error is coming from SP side URL, you should look at SP side FWSTrace.log
Federation Starters 3
Usually the FWSTrace.log would tell you why it failed but there are cases where policy server is the one reporting an error.
In that case, you need to track the same TransactionID from the respective smtracedefault.log and you should find the reason why.
You must ensure you have the correct profiler setting used for smtracedefault.log(which you would also find in the blog article too).