Here is how I did it

string sDateXDaysAgo = DateTime.Now.AddDays(-10).ToString("yyyy-MM-dd");
sFilter = "?%24filter=DateOfLastActivity%20ge%20" + sDateXDaysAgo + "%20or%20DateLastMaintained%20ge%20" + sDateXDaysAgo + "&%24select=CustomerNumber%2CTerms%2CCreditLimitCustomerCurrency%2CBalanceDueInCustomerCurrency%2CBalanceDueInFunctionalCurrency";

What this does is created a date string in yyyy-MM-dd format. It's how the string is required when using the web API.

Here is how I did it

string sDateXDaysAgo = DateTime.Now.AddDays(-10).ToString("yyyy-MM-dd");
sFilter = "?%24filter=DateOfLastActivity%20ge%20" + sDateXDaysAgo + "%20or%20DateLastMaintained%20ge%20" + sDateXDaysAgo + "&%24select=CustomerNumber%2CTerms%2CCreditLimitCustomerCurrency%2CBalanceDueInCustomerCurrency%2CBalanceDueInFunctionalCurrency";

What this does is created a date string in yyyy-MM-dd format. It's how the string is required when using the web API.

Okay, we will try to use this logic. Thank you!

It is working now)
Thank you a lot!

Hi Andrew1986, if the above suggested answer helped, please do mark it as verified  for the benefit of others in this forum :). Thank you!

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Could you please help with the following issue?
http://{BASE_URL}/Sage300WebApi/v1.0/-/SAMLTD/CS/CSCurrencyRates?$top=1000&$filter=DateOfLastActivity gt 1970-01-01

We try to receive currencies and rates. To receive the last data we use the filter in the request. But we received an error:

How we can apply data filters correctly?

You should post a new question really but, to answer this, there is no field on the CSCurrencyRates endpoint called DateOfLastActivity so you won't be able to filter on it.