I also got the same request.
Payment of Biometric Fees
1. You can pay immigration fees online with a Visa, MasterCard or American Express credit card if you have access to a computer with an Internet connection, Adobe Acrobat Reader software, and a printer.
2. This fee must be paid at the following link:
https://eservices.cic.gc.ca/epay/.
3. Click “Continue” at the bottom of the first page.
4. Select “Immigration” then under “Other immigration services”, select “Biometrics”. Note: “If you qualify for the “family” or “groups of performing artists” rates, only enter “1” into the ‘Quantity’.
5. Select the fee that applies to your application.
6. Click “Submit” and complete payment.
7. Once completed, send the payment receipt via the IRCC Webform at the following link:
https://secure.cic.gc.ca/enquiries-renseignements/canada-case-cas-eng.aspx.
Look at step 7. Once you paid the fees. You should have got the receipt . you have to send that receipt through this link ( https://secure.cic.gc.ca/enquiries-renseignements/canada-case-cas-eng.aspx ) to them.
That is a must step.