This article describes how a spend plan approval limit is checked
Spend plan approval limit is based on per each payment in the schedule.
Example: Spend plan approver has 50 000 approval limit and payment schedule is created for 12*20 000, this will total to 240 000.
Spend plan approver is able to approve the plan since none of the individual payments are over the approver's limit.
If any of the monthly payments are over 50 000 then the spend plan approver is not able to approve the plan. The approval limit is compared against the highest payment in the schedule.