Hi @fabio and welcome to the Community!
There are a few reasons why a welcome flow may not be sending the subsequent emails, but the cause varies greatly depending on the use case.
Firstly, is your list set up for Double vs. Single opt-in? If the list is set to double opt-in, your contacts must complete both steps before they will move through the flow. A profile is created for them in the list as a placeholder, however until they complete the steps they will not be marked as consenting to your marketing and therefore not move through the flow. More on this here:
Additionally, if subscribers were added before the flow went live, they won’t be included unless you opt to back populate the flow:
I hope this helps to clarify, and thanks for using the Community!
- Brian