The global parameter Theo describes can be found in

Settings > Technical > Parameters > System Parameters

This can only be accessed when in 'debug' mode, add url parameter ?debug after web in your browser address bar.

You have to create a new record with

key:    report.url

value:    http://localhost:8069

Further discussion here.. https://github.com/odoo/odoo/issues/2934

I want to give my 2 cents on this!

If you are loading your instance in port 80, you should've probably added the iptable record in your system. Then you've tried to print an invoice and everything is screwed. Ok!

Because you've changed the URL we need to say Odoo where are the assets now and because the project doesn't know anything about the iptable record you need to specify where the assets (css) are, so adding the following record to your system global parameters will solve the issue. 

Go to debug mode, either by adding the `?debug` parameter at the end of the URL or clicking in the profile at the top right and then on About. You'll see a popup with a button that says `Activate debug mode`. If you don't see it, you're not logged in as Administrator!

Go to Settings > Parameters > System Parameters

Add the following key/value:

Key: `report.url`

Value: `http://localhost:8069`

Those exact values! localhost is not a placeholder, use that exact same URL!

Try to print an invoice ;)

You're welcome!

Actually if you are sitting behind some kind of proxy (containerized odoo/ngix/squid etc) you need to set a global parameter 'report.url' = 'http://localhost:8069' and it will work like a charm all the time.

Regards

Theo

If you imported a database from another domain, it could be that web.base.url​ is set to the old one.

Here's how to update this using psql:

psql -d $LOCAL_DB -c "UPDATE ir_config_parameter SET value = '${NEW_BASE_URL}' WHERE key = 'web.base.url'"