Zollverien or Zollverein: How To spell?

The word Zollverien is misspelled against Zollverein, a noun meaning "Literally, a customs union; specifically, applied to the several customs unions successively formed under the leadership of Prussia among certain German states for establishing liberty of commerce among themselves and common tariff on imports, exports, and transit."

Word contains consecutive vowels 'EI' in between alphabets zollver & n is misspelled as 'IE'
Wrong Spelling:  zollver-ie-n 
Correct Spelling:  zollver-ei-n 
Find more incorrect spellings of Zollverein to spell right way.