Hi @abm, thanks for your reply,
A more precise description is the following:
There is a variable called a numeroFacturaRegistro of type string which is declared or initialized with an empty value

Later we have an array of objects, like this:

Within which for each object of the array you have a property called "Factura" (A reference is made later on this property)
It is necessary to make a cycle that runs through this array of objects to send emails, within this cycle initially the current item is shown in a compose action. We can see that for iteration 1, this property has the value "FE 31".

After this, the variable numeroFacturaRegistro is cleaned

Later the value of "factura", that is "FE 31", is saved in this variable
Edition mode of the action:

Execution mode of the action:

After this, by means of a compose action it is verified what the real value of the variable is:
Edition:

Execution:

Later, this data is taken into account to send an email to a customer.
Until this first iteration of the For Each cycle, everything goes according to the flow without problem.
The problem occurs in the next iteration (No. 2).
Starting again by referencing the current value of the current item in the cycle, you can see that now Invoice has the value of "FE 37":

Then, again the variable numeroFacturaRegistro is emptied

And then it is assigned the value of the "factura" property located on the current object in the cycle:

Apparently up to this point the variable numeroFacturaregistro has the value "FE 37", but when arriving at the compose action, in which direct reference is made to the variable, the value that actually stored the variable is shown, which was the one it had in iteration 1 of the cycle:
Edition:

Execution:

It is really confusing since no error is shown when assigning values to the variable.
Greetings.