The In Transaction replication process can be initiated either automatically (because the user or an automated process has modified data subject to replication) or OnDemand via AL code;
in this case, the write operation on the Source Peer table, or the call to the AL replication functionality, executes the SOAP call to the Target Peer within the transaction; as a result, an error in remote writing will cause a rollback on the Source Peer as well.
An important note: in the In Transaction mode, a single modification may require more than one call to the remote webservice.
In Transaction Replication to Multiple Target Peers: especially in the case of multiple Target Peers, using In Transaction replication can noticeably slow down the transaction on the Source Peer; use this configuration only if absolutely necessary and on connections with minimal latency.
In Transaction Replication in SaaS Environment: we remind you that Microsoft applies stringent limits on the number of incoming SOAP calls in a SaaS environment; when the Target Peer is hosted in a SaaS tenant, the use of in transaction replications must be carefully evaluated.