Why am I unable to create a metropolis center?

• Please check if your city is fully upgraded and researched all knowledges (also the new ones).

• Also, make sure that the city has 500,000 silver.

Why am I unable to link a metropolis with my metropolis center?

• If your city is not within 20 fields you can not link the city to your metropolis center and it is not shown in the list. 

• You should also check if your city is fully upgraded and researched all knowledges (also the new ones).

• Also, make sure that the city you want to link has 500,000 silver.