Common law application - what is "proof of common law" and how much is the payment?

[prsoon0595]

My girlfriend is applying for PR and is adding me as an accompanying common law partner. We sent webform and got a document list as response, but still have some questions:

1. The webform mentioned "proof of common law relationship", what is it? I did some online search and found Sponsoring your spouse, partner or dependent child, is this what we should follow? I can see it asks for IMM5589, IMM1344, and IMM5532 forms.
   1. Or, are they simply asking for evidence, and we don't need to fill out forms for now?
2. For proof of payment, we're given the payment page link. I'm see a fee of $1365 (processing fee ($850) and right of permanent residence fee ($515)), is this accurate? She has paid her application fees before, so what we're paying now is just adding me.

Many thanks! Attaching IRCC's response to our webform below in case anyone needs it:

After applying for permanent residence under the Economic class - Adding a family member

If you are the principal applicant of a permanent residence application already in process, you could add your spouse or common-law partner, dependent children, and their dependent children to your application, even if they were listed as a non-accompanying dependent in the initial application.

To do so, we invite you to send your add-on request by using the IRCC webform available on our website. You can attach the following forms and documents in the field reserved to that effect:

• A new Generic Application Form for Canada (IMM 0008)* with supporting documents,
• (If applicable) A Schedule A - Background/Declaration (IMM 5669) form,
• (If applicable) An Additional Dependants/Declaration (IMM 0008DEP) form,
• (If applicable) A signed Additional Family Information (IMM 5406) form,
• A copy of the birth certificate, marriage certificate or proof of common-law relationship,
• A copy of the family member’s valid passport,
• Police certificates for all countries where the family member over the age of 18 has lived for more than 6 months since turning 18,
• A letter of explanation (indicate “Add-on” in your letter), and
• If applicable, the proof of payment*.