Yesterday I migrated from v4 to v5. Everything is fine so far.
However, I cannot enter tax rates for expenses (A/R invoices). 
It shows me: “Item tax rates are disabled”.
Next to it is a button to the settings.
When I try to activate one of the 3 variants, I get the above error “404: Method not supported for this route”.
What am I doing wrong? Is there a solution for this?
(I have checked. There is a tax amount in the documents entered in v4).