You must be approved by Schwab to use your own DocuSign account.
Make sure the Schwab Form you want to map is eligible for digital-signature.
Your DocuSign account must allow you to create and send envelopes with SMS authentication enabled.
Once you have uploaded your fillable PDF form to your template, completed your mapping from the template to the PDF, enabled the DocuSign integration, and added DocuSign signature elements to the PDF, you can then choose the provider of the PDF.
Click on Edit PDF details in the upper right hand corner
In the provider drop down select Charles Schwab.
Selecting Charles Schwab as the provider will enable SMS Authentication, and forward the completed, signed document directly to Schwab. Any supporting documentation must be uploaded manually by you.
Note: Using your own Docusign account without approval from Schwab, or with a form not eligible for e-signature, will result in your form being rejected.