voltage to current Module
You've missed something crucial: the device needs a nominal 24 V DC to power it. The 4-20 mA signal is just a control signal.



Figure 1. MPPE technical data. Note 18 ... 30 V DC supply.



Figure 2. The 8-pin connector pinout.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 3. A likely connection diagram.

You haven't (for some reason) posted a link for the 4-20mA module so we don't know whether it is current sourcing or current sinking. The Festo documentation is vague too but I suspect it's current sinking so you have to drive 4 - 20 mA into the setpoint pin. That means your driver has to source that current. You may need to call Festo's tech support.