If you completed part 3 of TP-59-S-V then you do indeed need to fill out TP-64.3 as it was provided to you by your employer.
The issue (described in this post: https://turbotax.community.intuit.ca/community/troubleshooting/discussion/error-on-quebec-form-when-...) arises if you only completed part 1 and 2 of TP-59-S-V in which case you DON'T need the TP-64.3.
You can find TP-64.3 by searching the forms in TurboTax but you need to have it completed by your employer for you.
