Late Fees AFTER Notice to Pay or Vacate provided
I provided a tenant with a 3-day Notice to Pay or Vacate. The total amount is based on the back rent due, plus all late fees incurred up to the day I provided the notice. Per the lease I have an initial late fee, then a daily late fee after the initial fee. My question is, do the daily late fees continue to pile up after the 3-day notice to pay or vacate is provided (meaning if its $20 additional/day, and they pay on the 3rd day do they need to pay what was due plus $60?), or does it stop adding up, and they have a set amount to pay in the 3 days? I have done numerous google searches and can't find an answer to this part of my question. This is in Texas, btw. Thanks for all help in advance.

First question is what does TX allow as far as late fees? That should be in your state tenant-landlord laws. Second question is what does your lease say (assuming it is state-law kosher)?
The late fees are in the lease are laid out and in accordance with any state laws/regulations. They build up on a daily basis as rent is late. I just don't know how to apply, if at all the late fees once a notice to pay or vacate is provided.
That varies from state to state. Check Texas' landlord/tenant laws

@Reece Bierhalter. Late Fees should accumulate. i.e. $50 Initial PLUS $10 / Day paid on the 10th would be $150 in late Fees.
If you have already served the Notice to Vacate, and are proceeding to JP Court for eviction, my experience has been, the JP will not allow you to collect late Fees, only the Contract Rent. Your mileage my vary with a different JP Court.
Broker Texas (#396115)

Continue charging the late fees until they pay in full or vacate.
If you end up in court, the judge will not award late fees but that doesn't mean you should stop charging them.
Thank you for all the answers. Tenant paid up with late fees on day 3, just so I don't leave you all hanging.