After the exercise is completed (payment is processed), the system generates a share-type security for the exercised option grant. Click on the clipboard icon in the top right corner of your screen (next to your name) to accept the shares.

Go back to the portfolio page and click on the share ID to access its page, then click on "Upload 83(b)":
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Download the pre-filled 83(b) file, fill in the remaining information, sign it, and re-upload it to Pulley:

Follow the instructions in the downloaded PDF file to mail your 83(b) election to the IRS.