Merge union?

How would I merge a union to have more options seeing as union doesnt have merge method?

Base Union

const payment_methods = type("'credit_card' | 'debit_card' | 'eft' | 'apple_pay'  | 'samsung_pay' | 'visa_checkout'")

const payment_methods = type("'credit_card' | 'debit_card' | 'eft' | 'apple_pay'  | 'samsung_pay' | 'visa_checkout'")

Extended Union

const payment_methods_south_africa = payment_methods.merge("'zapper' | 'capitec_pay' | 'mobicred' | 'mukuru_pay' | 'snap_scan'")

const payment_methods_south_africa = payment_methods.merge("'zapper' | 'capitec_pay' | 'mobicred' | 'mukuru_pay' | 'snap_scan'")