Add flow expression to update item

Question

Based on the workflow expression created below, how can I can add/integrate it with update item in a SharePoint website?

Purpose: I would like to tell the SharePoint website that whenever a new row (every time add new item is clicked in edit grid view) is added, auto generate the next column (Reference Number (datatype numeric) value based on the previous value which for example is 10321.

reference_number column in descending order:

For example, let's say the last reference_number value is 10132 then, whenever the user clicks on add new item SharePoint should autogenerate the next reference_number which in this case would be 10133. Thus, each time add new item is clicked, the reference_number will be autogenerated by adding 1 to previous/last value.

How can I setup update item?

Error:

Unable to process template language expressions in action 'Initialize_variable' inputs at line '0' and column '0': 'The template language function 'add' expects its first parameter to be an integer, a float or a decimal number. The provided value is of type 'Null'. Please see https://aka.ms/logicexpressions#add for usage details.'.

Expression:

add(triggerOutputs()?['body/reference_number'], 1)

Current workflow:

Updated workflow:

Answer 1

Use power automate flow like below to get the last highest value in reference_number column and then update newly created item:

Use correct "internal name" of your reference number column in "Order By". You can get the internal name of your column by following this article: How to find the Internal name of columns in SharePoint Online?

In "Initialize Variable" action, use expression like:

add(outputs('Get_items')?['body/value']?[0]?['reference_number'], 1)

Then use this variable to update the reference number column using "Update item" action.