What happens when I import the same file twice in Zoho Invoice? Will the already existing data get overwritten?

When you import the same file twice, the entries of the file won’t replace the already existing files. Instead, it skips the existing entries and imports the ones that are new.

PS: This rule does not apply if you choose “Overwrite” option while importing data in the Contacts and Items modules. By clicking this, all the values in the existing records will be replaced with the imported ones and cannot be restored