Multiplus2 will not turn on when connected to ve bus on cerbo

i have a multi plus 2 when i connect the ve bus to cerbo gx the inverter will not turn on. if i connect ve bus after turning on all is ok untill i turn multi plus off then it will not turn back on untill i disconnect cable

Check the switch setting of the multi in the cerbo:
Setting in remote console
If there is “Off” selectrd, the multi doesn’t turn on

The switch setting is on, if i turn it off I cant turn it on again

Maybe your issue is:

https://www.victronenergy.com/media/pg/Cerbo_GX/en/installation.html

If you power the Cerbo GX from an AC adaptor connected to the AC-out port of any VE.Bus product (Inverter, Multi or Quattro), then a deadlock will occur after the VE.Bus products are powered-down for any reason (after any operational fault or during a black start). The VE.Bus devices will not boot-up until the Cerbo GX has power …but the Cerbo GX will not boot-up until it has power. This deadlock can be rectified by briefly unplugging the Cerbo GX VE.Bus cable at which point you will observe the VE.Bus products will immediately begin to boot-up.

If so, either feed your cerbo from the battery, or purchase a dedicated micro-UPS for the cerbo. (few bucks on amazon) I did the later, because my Batteries are not discharging without BMS communication, so directly attaching the cerbo to the battery does not resolve this.