Difference of values in impression attribute from campaign summary report and top campaign content report

I'm not sure why, but the impression number from the Top Campaign Content Report does not match the impression number from the Campaign Summary Report.

my campaign ID: 10730350

When I call the endpint:

/api/1.0/audibene-fr-sc/reports/campaign-summary/dimensions/campaign_breakdown/?start_date=2021-06-01&end_date=2021-06-01

The response is:
[
{
"campaign": "10730350",
"impressions": 277475,
...
},
...
]

And when I call this endpoint:

/api/1.0/audibene-fr-sc/reports/top-campaign-content/dimensions/item_breakdown/?start_date=2021-06-01&end_date=2021-06-01&campaign=10730350

The response is:

[
{
"impressions": 142764,
...
},
{
"impressions": 75512,
...
},
{
"impressions": 59172,
...
},
]

When I aggregate up the item impressions, the result is 277448, which differs from 277475 (the figure I obtained from the previews endpoint), thus I'm not sure why the disparity exists or which number I should consider.