Can't change power setpoint with modbus TCP

Good morning,
I run a 3 phase system (3 Multiplus II, a GX color control and 8 pylontech batteries) with own made ESS control. I send the power setpoint for each phase by modbus TCP (register 37, 39 and 40). The register is well write (check with modbus poll) but the charge power doesn’t change.
I set the ESS to “external control”. Charge and discharge registers are set to 0.
Does someone have an idea ? Do I have to change a parameter somewhere ?
Could it come from the batteries ?
Thanks for your help !

From the docs, those setpoints are taken into consideration when the batteries are full and they disabled charging. I.e. ESS mode 3.
This is the case?

The batteries are 93% full, I use ESS mode 3.

OK.
Registers 37, 39 and 40, as you wrote, or 37, 40 and 41 ?

37, 40 and 41.
I use 38 and 39 to enable charge and discharge

It start working today at 6am, I did not change anything. But it works.

And the SOC at that time was ?..

93 %, it did not change between yesterday and the moment the regulation start working (now it’s lowering, that’s what I want).

I find the problem ! It was because of register 71, when this register is set to 1, the setpoint is saw as a limit, no a real setpoint. I don’t know how ad why this register value change but when I change it manualy, I get the same behaviour.
So to control the inverters, register 71 must be set to 0.
Have a nice day !