For example unlimited person shall be analysed.

This prevent creating open order when adding person with business template

validate_action calls check consistency, which asserts existence of open order,
and as it uses catalog related key, such one have to be indexed correctly.

Also expose payment in sequence.

The sections are not definitive on Payment Transaction, so inventory API will
allow to easily find the payments, by checking balance with given states.

Payment shall represent fact that customer will give money.

This documents allow to lower balance of customer, Payment Transaction shall
not be used.

It is required in order to have them accounted.