If I understand correctly, you have 2 tables
Project
Units
Upon save of a Project you want to kick off a workflow that'll create child unit records based on the value of the "Number of Units" field in the Project record.
I had a similar use case and also realized that there was no way to loop x number of times in a pipeline, however this could be done in a webhook on the Project table with a call to the API_ImportFromCSV on the Units table.
The payload would be generated using a jinja loop inserting multiple identical records into the units table with the current Record ID as the Related Project on the unit
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Simon H
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