At present, providing an e-sign is the only way to sign the advisory agreement. In case your mobile number is not linked to your Aadhaar then you will not be able to e-sign.
We will soon come out with a process to sign the document using other methods as well.
Until then, you can select the "Do it Later" option (this is a temporary option we are providing)
You can refer to this FAQ to understand why this is required.