The reason for the zero tax is that OK uses the amount of state income in box 16 of your W2. Since there is no income reported there for OK, the tax is zero.
To pay what you owe OK for 2020 you will need to revisit the "Job (W2)" topic in the federal interview. Edit the W2 and go to the state boxes (15-17). In box 15 select OK and put in the federal ID number from your W2 in the state ID box. In box 16 you need to put the prorated amount of wages for OK. Use your W2 box 1 amount and multiply it by 5 and divide by 12 to get 5 months of your wages for OK.
If using a desktop version switch to the step-by-step view and follow the same procedure.
For your 2021 taxes it sounds like you employer has adjusted and your W2 should reflect the correct amounts next year.
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