Error:
....
File "c:\program files (x86)\arcgis\desktop10.7\arcpy\arcpy\analysis.py", line 1281, in Frequency
raise e
ExecuteError: Failed to execute. Parameters are not valid.
ERROR 000824: The tool is not licensed.
Failed to execute (Frequency).
....
Reason:
Calculation of the number of observations assigned to an EO to determine if the EO fields should automatically be updated (count = 1) or requires user input (count > 1) requires the Analysis toolbox.
The problem is found on line 111:
Frequency_EOIDs = arcpy.Frequency_analysis(EO_ID, frequency_table, "EO_ID", "")
The Analysis tool is available with the Basic license in ArcPro but the Advanced license is required in 10.3 and 10.7.
Solution:
Run the ArcPro version of the Observations toolbox instead to avoid licensing issues.