Hi CRMUser789,
the first steps are already done, when you have mapped the lookup fields in the Classic Editor - Lead entity - 1:N Relationship - account_originating_lead - mapping:

Click on New and add the lookup field for Lead and Account entity:

The important step that the mapping can be resolved is adding a key to your custom entity Category (In my example test entity - you can either add the key in classic editor or in make.powerapps.com - see screenshots below). In the example I have select name as field for the key. As a key requires a unique value in the field you can either select another field or a combination of multiple fields as key.

Adding Key in Classic Editor

Adding Key in Maker Portal
Once the key is added you can select a value in your lookup on the lead entity and after qualifying the lead, the same record is selected in your lookup on account entity

Best regards,
Joergen
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