Changes to Create contract

request property payment_frequency was restricted to a list of enum values

the payment_frequency request property type changed from no type to string

the transaction_ids/items request property type changed from no type to string

the account_id response's property type changed from no type to string for status 201

the id response's property type changed from no type to string for status 201

the payment_frequency response's property type changed from no type to string for status 201

the transactions/currency response's property type changed from no type to string, and format from no format to ISO 4217:2015 for status 201

added the new half-yearly enum value to the payment_frequency response property for the response status 201

added the new monthly enum value to the payment_frequency response property for the response status 201

added the new quarterly enum value to the payment_frequency response property for the response status 201

added the new yearly enum value to the payment_frequency response property for the response status 201

added the new half-yearly enum value to the request property payment_frequency

added the new monthly enum value to the request property payment_frequency

added the new quarterly enum value to the request property payment_frequency

added the new yearly enum value to the request property payment_frequency

the currency response's property default value EUR was added for the status 201