Would you teach me which is corret in the blank?

spending

Spend, spending, or expenditure would all fit. Spend (noun) is a common usage in trade journals.

Loyalty programs are proven to increase customer lifetime value by up to 30% or more by increasing visit frequency, increasing spend per visit, ...

Desserts are also a good way of increasing spend, have free samples at the till that they can have while waiting.

...they must now focus on retaining and growing market-share through increasing spend-per-meal and repeat business