Allow negative balance for PTO when Employee applies directly but not allow for the FMLA-PTO plan?

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Our clients have the ability to apply the FMLA-PTO where the Employees get paid during the FMLA period if they have PTO balance. But once the PTO balance hits zero, then it should be unpaid for the rest of the FMLA.

But the clients also want us to allow negative balance to a limit when an employee applies for PTO directly as a plan.

When I use the same configuration, the PTO payment gets continued even after 0 for the FMLA-PTO plan.

Please let us know if we can achieve this where the PTO doesnt go negative when its part of FMLA-PTO plan