How can I only receive data from selected serial numbers

[buran]

Unless you are able to filter serialNumbers in the API requests your approach is correct. The problem that in the JSON serialNumber is str and in your ignore list - int

# assuming you have properly converted the json response
json_response = [
{
"serialNumber": "121718037628",
"lastReportDate": 1549920259,
"devType": 1,
"lastReportWatts": 18,
"maxReportWatts": 18
},
{
"serialNumber": "121718037534",
"lastReportDate": 1555635154,
"devType": 1,
"lastReportWatts": 108,
"maxReportWatts": 187
},
{
"serialNumber": "121718037683",
"lastReportDate": 1555635148,
"devType": 1,
"lastReportWatts": 117,
"maxReportWatts": 197
}
]

ignore_set = {'121718037628',} # that is actually a set

for inverter in json_response:
    if inverter['serialNumber'] not in ignore_set:
        print(inverter)

Output:
{'serialNumber': '121718037534', 'lastReportDate': 1555635154, 'devType': 1, 'lastReportWatts': 108, 'maxReportWatts': 187}
{'serialNumber': '121718037683', 'lastReportDate': 1555635148, 'devType': 1, 'lastReportWatts': 117, 'maxReportWatts': 197}
>>>