For share transactions that have secondary transactions records, the most recent record will need to be deleted first before the original record can be deleted.

For example, where a transaction has been repurchased, the repurchase transaction will need to be deleted before the original transaction can be deleted.

This is also the case for Transfers and Conversions

In the Share Transactions screen, for transactions that have secondary transaction you can see the dependent transaction IDs to the right of the status
Select the three-dot menu on the secondary transaction and select Delete
You will be asked to confirm that you wish to delete this transaction. Select Yes and the transaction will be removed
Once the secondary transaction has been deleted, you can delete the original transaction by selecting the three dots menu and selecting Delete and confirming that you wish to delete the transaction

Deleting a share transaction