See if there's a HEVRA garage near you, they might be able to fix it cheaper.

HEVRA Europe- Electric and Hybrid Car Repairs

www.fixev.org

 

seems you can get used ones for around 600euros - wouldn't you just have to change VIN details with either CAN CLIP or even DDT4ALL (if the VIN details do need changing)
These as example:

https://www.gpa26.com/en/reference/179764

RENAULT 296G93381R, 296H27355R ZOE (BFM_) 2018 SPANNUNGSWANDLER | eBay

RENAULT 296G93381R, 296H27355R ZOE (BFM_) 2018 SPANNUNGSWANDLER | Auto & Motorrad: Teile, Autoteile & Zubehör, Sonstige | eBay!

www.ebay.com.sg

 

Check if your insurance covers it, in sweden Renault insurance (and many other insurance companies too) covers up to 150.000 km or 10 years. Motor and charging system is included.
Contact your road insurance company and ask them what is included.

 

Thank you very much for your answers, but at present there is no longer any guarantee.

They say that you have to replace the entire inverter, others say that it can be repaired, and my question is whether you can put a second hand one.

Right now the car has 78% soh of battery and I don't know if it's worth investing more than 4000 euros to repair it.

 

You can fit a second hand inverter but only by physically moving across the chips containing the vin. They are write once protected.

However the last one we did a few weeks ago the used inverter was £300 and new from Renault £550 and its about 12 hours labour to take the whole stack out and replace the inverter due to the amount that has to be taken out to get the stack out then the bus bars etc to get off to remove the inverter - best to fit a new inverter anyway as a used one might just fail like the old one!

Cheers