Hello,

You need to make sure you have a currency rate that is older or on the first day of the invoice accounting period. You can test it by setting a currency rate in a past year.

Best, 

I have encountered this error. The solution is to make sure you have at least two currency rate entries for the base currency and the counterpart currency. i.e. Lets say you want to convert from Dollar to Naira. You will create two currency rate entries for Dollar and two currency rate entries for Naira.  The currency rates must be set with a date that is, ON or before the order date. That is just the solution. I had to debug it on my development environment to figure out why the system raises that constraint error, despite having entered a single currency rate.  Thanks. Please vote my answer if it solves your problem.

Note: Path to Currency Configuration is: Accounting->Miscellaneous->Currencies

Hello Diego,

Go to accounting, miscellaneous, currencies. There yoi can check that you have the rate properly set-up for the period you are posting into, for the currency of the document you are trying to save.

Note that sometimes odoo does not get the date properly so you better choose the date from the drop down menu to make sure, you are posting in the right period.

Good Luck!