The fix is to remove a variable mapped to that field.
There error indicates the field “Appointment ID” is computed, which means that field is a formula, rollup, lookup, autonumber, or any other “computed” type.
Computed fields calculate their value based on something else.
They are read-only.
You cannot populate them in a Zap step.
TIP: Try sharing your screenshot with ChatGPT and asking for help explaining and understanding the error.