I have a google spreadsheet consisting of different months on each tab. Every month, I add a new tab and another 50-75 rows. There are many tabs. There is a cell on each row which calls a custom function, like this:

=myFunction(A1)

The problem that I am having is that I am getting the following error:

error: Script invoked too many times per second for this Google user account.

What can I do to prevent this error from occurring? Is the problem because there are too many tabs, or too many rows per tab?

There must be a way to prevent the function from having to run more than once. Thanks.

EDIT: Here is a shortened version of the function that is called:

function myFunction(expense) {
if (
  InStr(1,expense,"CPC SCP") ||
  InStr(1,expense,"CPC/SCP") ||
  InStr(1,expense,"xxxx")
  )
  { category = "5530 - Postage Expense" } 
 
  else if (
  InStr(1,expense,"PRE-AUTHORIZED PAYMENT") ||
  InStr(1,expense,"xxx ")
  )
  { category = "9999 - Payment" } 
  
  else if (
  InStr(1,expense,"PURCHASE INTEREST") ||
  InStr(1,expense,"RETURNED PAYMENT FEE") ||
  InStr(1,expense,"xxxx")
  )
  { category = "5070 - Bank Charges" } 

else { category = "Not Sure" }
    
return category;  

}