Hello,
I am trying to use a transaction in a flow, so I call
pub.art.transaction:startTransaction

Then I make several requests over several connections

then I call commitTransaction.

On the commit call, I get the following error:
[SCC.0121.0034E] commit failed: more than 1 local trans enlisted. xid = [FormatId=45744, GlobalId=magellan/1200670154111, BranchQual=1] rxid = {2}

I am 100% sure that I have opened no other transaction.
Some of my adapters are set to Local_Transaction, others to NO_Transaction

Could that be the problem?

Yes. The documentation states that only one connection within an XA transaction can be configured with local transaction.

Ok I had two adpaters set to LOCAL_TRANSACTION, it works now, thank you!