I have also paid for the Biometrics fee at the same time I prepared and submitted my application. I received a "Biometric Instruction Letter" from IRCC in May.
Printed that out and brought it to VFS Global. A very straight forward process.
You should do it step by step. They are saying that you didn't pay for the Biometrics fee yet, so make sure you pay for that and send them the receipt (proof of payment). Then they should send you the "Biometrics Instructions Letter".